Inside the Mind of Dear X: A Psychological Breakdown of Yun Jun Seo
A deep dive into Yun Jun Seo’s psychology in Dear X, unpacking his trauma, contradictions, and quiet self-destruction.
Aya’s Introduction
When I first read Dear X, I thought I had it figured out. I had my opinions. I had my frustrations. I had my “why are you like this” moments. And honestly, I was ready to just write my review and move on. But before I did that, I started looking a little closer at the characters—trying to understand why they acted the way they did, why certain choices kept repeating, and why everything felt so emotionally messy. And… yeah. That opened up a whole new world.
The more I looked into Baek Ah Jin (played by Kim You Jung), Yun Jun Seo (played by Kim Young Dae), and Kim Jae Oh (played by Kim Do Hoon), the more I realised that none of them are “just toxic” or “just bad” or “just frustrating.” They’re all products of their environments, their trauma, their relationships, and the emotional tools they never learned how to use. So I decided to put all of that research, thinking, overanalysing, and emotional spiraling into these extended character breakdowns. This is for anyone who was just as curious as I was, but didn’t feel like going down a ten-tab research rabbit hole (because honestly… I get it).
One important thing before we dive in: I’m not a psychologist, therapist, or mental health professional. Everything in this analysis is based on personal research, reading, and my own interpretation of the story. I use psychological terms to help explain patterns and behaviours—not to diagnose these characters or present anything as medical fact. This is just me trying to understand them more deeply, make sense of their choices, and share that process with you. I’d also like to mention that I am in no way justifying their actions. Understanding the reason behind certain actions doesn’t justify the actions. People were killed. Lives were ruined. Those facts won’t ever be erased no matter how deep we dive.
We’ve successfully finished Baek Ah Jin’s Analysis (read here!). Now let’s get into Yun Jun Seo.
*Table of Contents will be in the bottom right corner (because it’s a lot 🤭)*
Introduction: When Love Becomes Identity
Some characters don’t fall apart all at once.
They unravel slowly, quietly, and in ways that are easy to mistake for love.
Yun Jun Seo is one of those characters.
On the surface, his story looks like devotion. It looks like loyalty without limits, sacrifice without hesitation, and love that never wavers no matter how much it costs him. He stays when others would leave. He absorbs what others would reject. He endures in ways that feel rare, even admirable. And because of that, it’s easy to watch him and think: this is what loving someone completely looks like.
But the deeper you look, the more that image starts to fracture.
Jun Seo’s story isn’t about healthy love, and it isn’t about romantic devotion in the way it’s often framed. It’s about what happens when a person builds their entire identity around someone else. It’s about what happens when loyalty becomes obligation, when endurance replaces communication, and when self-sacrifice slowly turns into self-erasure. What looks like strength on the outside is, underneath, a pattern shaped by trauma, dependency, and a desperate need to make suffering mean something.
This analysis isn’t here to excuse his actions or to villainise him.
It’s here to understand him. To look at the psychology behind his choices, the patterns behind his loyalty, and the internal logic that made every decision feel inevitable from his perspective. Jun Seo isn’t confusing once you break him down. He’s consistent. Painfully so.
And once you see that consistency—once you understand the way his identity, his love, and his survival all intertwine—you start to realise something uncomfortable:
Jun Seo didn’t suddenly become tragic at the end.
He was always heading there.
Part I — Yun Jun Seo’s Psychological Foundation
Yun Jun Seo’s Childhood Psychology: The Foundation of His Identity
Understanding Yun Jun Seo and all his actions begins with understanding who he was becoming before Baek Ah Jin meets him. Even though the drama may not have spelt it out, based on his vulnerability, his psychology screams emotional inconsistent caregiving; a mother who is controlling, volatile, and conditional; a love that is tied to behaviour (“good son” vs ”bad son”); and fear of abandonment.
Kids raised like that usually crave approval, struggle with internal moral clarity, they are usually highly suggestible to emotional narratives, and confuse intensity with love. When Ah Jin enters his life, he’s already primed.
So why was he so easily manipulated?
The answer to that is because Ah Jin didn’t manipulate Jun Seo with lies alone, but with emotional truth wrapped in distortion. When she told him: “Your mother is bad”, “She doesn’t really love you”, and “I’m the only one who cares”, it was the environment and experiences he endured that made those effective. Why? Because his mother was abusive, what he lived through matched Ah Jin’s framing, and Ah Jin filled the caregiver role that his mother failed at. That wasn’t brain washing, that was attachment replacement.
The Solidifying Moment: The Bathtub Incident
Once Jun Seo witnessed his mother trying to kill Ah Jin, this proves that Ah Jin was not only right, but confirms that he was powerless. Psychologically, this does a lot. For one, his internal belief system splits to mother= bad; Ah Jin= good. Once a child collapses morality into binaries, it’s almost impossible to reverse. This is what traps him to her for his entire life. So even when he knew what she was doing was wrong, Ah Jin (to him) wasn’t wrong.
She didn’t need to manipulate anymore because that’s what long-term trauma bonding does. Ah Jin had trained him that love equals sacrifice, loyalty means silence, and protection requires self-erasure. So by adulthood he anticipated her needs, he acted without instruction, and carried her guilt for her. He essentially became like her moral sponge.
On top of his moral collapse, he also gains saviour guilt. So even though he was also a child, he failed to protect Ah Jin and she nearly died. Because of that, he internalises “if I had been stronger, she wouldn’t have suffered.” That guilt never leaves him.
What followed was trauma bonding. A trauma bond can form when: fear + attachment + rescue happen together. He watched her jump out the window + He called 9-1-1 + She survived. For him, Love = terror + responsibility + loyalty. When he later says “I’ll never leave you again” in the hospital, that’s not romance. That’s identity fusion. From that moment on (and we see it throughout the show), his worth became tied to staying, leaving felt like murder, and disloyalty was the same as death. That’s why he can’t leave no matter how she treats him. Leaving, for him, was like moral failure.
Jun Seo wasn’t obsessive because he was weak. He was a child who formed identity under terror, a boy who replaced morality with loyalty, a man who mistook endurance for love, and someone who never learned how to exist outside of another.
His tragedy wasn’t loving Ah Jin. It was that loving her became the only way he knew how to be alive.
Jun Seo’s Adulthood: Murder And Baek Ah Jin’s Father
Throughout the drama, Jun Seo consistently expressed his willingness to do everything for Ah Jin but murder. But why? You might be thinking it’s because it’s murder but it’s deeper than that.
Despite everything, Jun Seo had one remaining moral anchor. His loyalty may have been extreme but it wasn’t a total erasure of who he was. If Jun Seo killed, it would make his childhood promise meaningless. His core belief was, “I stay so no one else has to bleed.” Murder would’ve broken that belief.
If he kills, he becomes like the adults who failed them, he proves that survival requires becoming monstrous, and he loses the moral ground that sustains his identity. For Jun Seo, murder wasn’t just an act, it was identity annihilation.
With all this in mind, it leads me to my next scene breakdown: Ah Jin’s father and the night of his murder. If you think back to that night and the aftermath that followed, we see how Jun Seo heads to the apartment, finds Ah Jin there, and hits the father in the head again. You may be wondering, why would he do that if he would never commit muder? And the answer is simple: the father was already dead.
Jun Seo did not hit him to kill him. That’s what’s important to remember. By the time Jun Seo swings the bat, he’s already checked that the father’s dead. What Jun Seo did wasn’t murder, it was authorship. Based on all of his actions and his desperate need to take the blame, he needed the scene to say “I did this” loudly enough that Ah Jin disappeared from the narrative, the responsibility transferred fully to him, and the moral weight landed on his body instead of hers.
This may seem to contradict the idea that he wouldn’t murder but here’s the key: Jun Seo doesn’t experience this as violence, he experiences it as correction. He was simply thinking, “I am making the story clean.” and absolutely justifies it because it’s for Ah Jin. In his internal logic, violence done for himself was unforgiveable, but violence done for Ah Jin became duty. Jun Seo didn’t want innocence, he wanted containment— a way to seal the damage so it didn’t spread to her.
This way, he could rationalise indirect harm. Directly killing would’ve meant choosing violence consciously, crossing from a protector to perpetrator, and opening irreversible destruction. Jun Seo survives by enduring, not acting. That’s the line.
So what if Ah Jin’s father had been alive and groaning? That’s simple: Jun Seo still wouldn’t have killed him. Jun Seo’s identity wouldn’t have survived him being the origin of death. Violence, yes. Murder, no. That line matters far more to him than he led on. If the father had been alive, he would’ve called for help while positioning himself as the aggressor and taken responsibility through confession.
The only thing he wouldn’t have done was deliver the killing blow. Why? Because Jun Seo doesn’t see himself as someone who ends lives but as someone who absorbs consequences. That’s why the scene works well for him: the father already being dead allowed Jun Seo to step into the guilt without becoming a murderer. It was the only version that would’ve allowed him to fully protect Ah Jin and remain psychologically intact.
So if the father had lived, Jun Seo would’ve taken whatever blame he possibly could that would’ve been enough for Ah Jin to no longer be visible— that’s the point.
This fact also pisses Ah Jin off. Why? Because if Jun Seo kills for her, his morality collapses, his loyalty becomes total, she no longer has to feel judged, and she proves that love = absolute sacrifice. His refusal constantly threatened her worldview. It said, “there is a line you cannot make me cross.” and that makes her feel uncontrollable, unpowerful, and exposed. That’s why she always threw it in his face like an insult.
Part II — Jun Seo’s Later Adult Years
The Book He Wrote on Her Life
One of my favourite parts about this show was how every action each character made was very telling and very fitting for their character’s psychology. For example, the book Jun Seo wrote. Despite being apart from Ah Jin for years, he still decided to become a writer to write her story. Why? Because the book was his way of making her suffering meaningful, it was his attempt to organise chaos into narrative, and his way of justifying his devotion. By turning her life into a story, he gave her pain purpose, he absolved himself of leaving, and positioned himself as the witness who stayed. For someone whose identity is surrounded by being loyal, that’s very fitting for his character. It wasn’t exploitation, it was memorialisation as coping.
Jun Seo and The Other Men in Ah Jin’s life
Around when he wrote the book was around the time other men started to get involved in Ah Jin’s life, so this would be the perfect time to clarify some things. I see a lot of comments and people loving his devotion and his love for her but it’s important to remember this: he didn’t mind her being with other men. Jun Seo didn’t love Ah Jin in a romantic sense, like people assumed. He was trauma bonded to her not romantically bonded to her. Let’s go through Ah Jin’s relationships to help with this idea.
Jae Oh
After Ah Jin and Jae Oh meet for the first time after Jae Oh gets out of prison, Jun Seo tells Jae Oh that he thinks Ah Jin would be better off with Jae Oh than him. This is one of the clearest signs that Jun Seo’s attachment wasn’t romantic love. He’s capable of saying, “If someone else can protect her better, that’s okay.” This tells us that his bond is sacrificial, not possessive. That his goal is containment of damage, not closeness. That he sees himself as expendable. This is the caretaker identity, not partner identity.
In Gang
After Jae Oh, we get In Gang. By this point in the story, Ah Jin has chosen In Gang, she stayed longer than promised, she’s built a life that doesn’t include Jun Seo, and his “I’ll endure and wait” strategy has failed. By this point, he’s starting to crack. Why? Because all that means is that his loyalty has not been rewarded, his suffering has not been meaningful, and his patience has not saved anyone. Therefore, his core belief, “If I stay, I matter,” is breaking.
So when he eventually confronts her that night at his house, it’s much more than him being upset that she stayed longer than a year. Emotionally, what he’s really saying is: “You weren’t supposed to replace me.” Not romantically, Existentially.
When he agreed to help her for that year, he wasn’t expecting her to prove that life works without him. And then comes the kiss attempt. When he tried to kiss her, he wasn’t thinking: “I love you. I want to be with you.” He’s subconsciously thinking “Tell me I still matter.”
That kiss would’ve meant “I’m still your person” “I wasn’t just a waiting room” “My loyalty wasn’t wasted.” It was his last-ditch attempt to reassert emotional relevance, special status, irreplaceability, and the old dynamic.
Then comes the question, “Why now? Why after an entire year?” because now the illusion is gone. For a year, he could tell himself that she’ll come back, that it’s temporary, and that he’s still central. Her staying effectively destroyed that fantasy. This is the moment he has to face the thought, “I’ve been sidelined permanently.” That’s usually when people reach for desperate intimacy.
The kiss wasn’t an attempt to “steal” her from In Gang. Because it wasn’t a romantic relationship. It wasn’t about building something. It was about not disappearing.
So how does this fit with his “usefulness love”?
Jun Seo’s version of “love” is: “I exist for you. Therefore I exist.” But she no longer needs him. So now, he loses purpose, his identity, and his emotional footing. What he wanted most through the kiss was him trying to reinsert himself into her emotional economy. “Let me be something to you again.”
To us, the scene feels awkward and uncomfortable. That’s intentional. We understand what a healthy relationship should look like. That scene was meant to show you that this is not romance. It’s collapse. We understand that a healthy Jun Seo would say “I’m hurt you stayed” “I guess this is really over.” “I hope you’re okay.” and leave.
But Jun seo can’t leave cleanly. Leaving means accepting that he was optional. And he can’t accept that. What makes this heartbreaking isn’t that he tries. It’s that even in his lowest moment, he still frames his need through her. He still can’t say: “I matter on my own.” so he reaches for her instead.
Do Hyeok
You may not have realised that Jun Seo didn’t care that Ah Jin got married because they were so far apart, but this continues to prove the fact that: Jun Seo’s bond to Ah Jin was not about possession. It was about meaning.
Her marriage doesn’t threaten his role because he never believed he was meant to “have” her, his role was to stay, not be chosen, and her happiness doesn’t invalidate his loyalty. The reason In Gang staying longer did threaten him was because it disrupted the “temporary” structure he relied on. Marriage gave the bond a clear ending and Jun Seo had already started to resign (more on this idea below!).
Part III — Jun Seo, His mother, his decent, and His later episodes
We eventually get to the part of Jun Seo’s story when his mom becomes more present and we really start to see his rapid decline to his inevitable death. First off, it’s important to note that Jun Seo never forgave his mother and by inviting her back into his life, we truly see just how bad it’s become. Now before we really get into it, let’s go through his decent while sticking to the storyline.
The Kidney Transplant
You may be wondering how I could say all of this if he gave her his kidney. That’s not hypocritical, that’s accurate. And we see its accuracy with what he says before and after. The kidney transplant wasn’t a one and done. It was a transaction. An agreement. Jun Seo agreed to the transplant only if his mother stayed away from Ah Jin and his grandfather. That right there showed us that he believes love = payment and that he uses leverage instead of trust. That was instrumental care, not emotional intimacy.
He doesn’t say: “I forgive you.” He says “I will give you my body if you obey my conditions.” That wasn’t cruelty though, it’s how someone raised on conditional love learned to operate.
Jun Seo’s Want For An Apology to Ah Jin
When Jun Seo wanted his mother to apologise to Ah Jin, it wasn’t about forgiveness. Psychologically, Jun Seo wanted his childhood narrative validated, his loyalty justified, and his trauma morally resolved. If his mother apologises to Ah Jin then it proves three things: Ah Jin was right, Jun Seo was right to choose her, and his lifelong devotion wasn’t misplaced. That apology would’ve retroactively saved his identity.
Discovering His Parentage
Then we get to the point when he discovers that he’s not his father’s biological son. What matters the most about this point is that he’s not even angry at his mother. He doesn’t even seem to care about her truth. That right there shows how disconnected he’d become from his mother. All he cares about is Ah Jin.
Learning that he wasn’t his father’s biological son triggered core shame, illegitimacy anxiety, and fear that his existence is a burden. Now add this: Ah Jin knew. But instead of anger, he feels relief through guilt. Why? Because guilt kept the trauma bond intact. If he blamed Ah Jin, he would’ve had to accept that she exploited him, had to grieve the bond, and had to admit that his life was shaped by manipulation.
So instead, he reframes it as: “I should’ve suffered more for her.” That way, he preserves the meaning of his devotion.
Is Jun Seo Toxic?
Before we truly get into the beginning of his identity crack, the final episodes, and his death, I felt like the best way to introduce those parts is by answering a comment I saw about him saying that Jun Seo was the toxic one, not Ah Jin. The commenter explained that Jun Seo assumed the worst of her, his love wasn’t selfless, he never tried to understand her, and only wanted to control her. The commenter then explains that when she pushed him away, he suddenly decided to expose her for revenge or anger and that his death wasn’t martyrdom. This is actually from multiple comments so let’s break it down. Is Jun Seo the toxic one?
Short answer: he’s not the problem, but he is a problem. There’s one thing that a lot of people have glossed over and that’s Jun Seo’s love was not purely selfless. It was conditional in a quiet, insidious way. The thing is, he never tried to understand Ah Jin as she was as an adult. He understood her past, her pain, and her damage. But not her agency.
In his mind, Ah Jin existed in two versions: the girl who was abused and needed protection, and the woman he hopes she’ll become once she’s “safe.” What he actually struggled to accept was the person she was in the present. So in a way, he did assume the worst of her but not because he thought she was evil. It was because he was terrified that if she was acting consciously, then her cruelty was real, her rejection was final, and that his devotion was never wanted. Seeing her as “someone who uses others” allowed him to hold only the idea that she’s just broken, not choosing. It was the emotionally safer option.
Then we get to the question about whether or not he wanted to control her. The thing is that he didn’t want to control her in the stereotypical domineering way but he did want to contain her. Control doesn’t always look like ownership. Sometimes it looks like moral positioning, sacrifice, “I know what’s best for you” and staying even when you’re not wanted.
Jun Seo’s control fantasy was subtle: “If I stay long enough, suffer quietly enough, and love her correctly, she will eventually return to the person I believe she is” That wasn’t malicious but it was self-centered. He wasn’t asking “Who is Ah Jin choosing to be?” He was asking “Why won’t she stop?” So in a way, he was hoping she’d change for him even if he’d never consciously admit to it.
Then we get to the part of the comment that claimed he suddenly decided to expose her. His decision wasn’t sudden. It was the result of accumulated guilt, exhaustion, identity fracture, and moral awakening that he could no longer ignore. Remember, his entire identity was shaped around being loyal. Choosing to betray Ah Jin and being disloyal was not a decision Jun Seo would’ve been able to make suddenly. He exposed her because he finally accepted that love without accountability is just destruction. That was the first independent moral choice he made in his entire life.
And this leads me to my next point, why he betrayed her instead of just leaving. The reason he couldn’t have done that was because leaving would’ve meant accepting meaninglessness. If he walks away then his years of devotion end quietly, his suffering changes nothing, Ah Jin continues unchanged, and his role in her life evaporates. That’s unbearable for someone whose entire identity is built on enduring for a reason.
*I just want to briefly clarify that I am aware that I mention him having multiple identities (loyalty, enduring, self erasure, etc.) and that’s not an accident. All of those, and any others I mention, all make up his identity: loyalty, enduring for a reason, self-erasing and anything else I mention falls under that loyalty umbrella.*
Exposing Ah Jun gave him narrative control, moral authorship, and a final act that forces consequences. His exposure wasn’t revenge, it was desperation for significance. “If I can’t save you, then I will stop you.” and that’s the pivot.
So why expose her if he was loyal and he knew it would destroy him? Here’s the most important fact: he was already done. By the time he moves back into his mother’s house, that’s not recovery, that’s regression. It was a man shrinking his world because he no longer planned to live forward. Exposing Ah Jin became his last meaningful action. The only reason the betrayal is “justifiable” to him was because he didn’t plan to survive it.
I go into much more detail below but I still wanted to help back up the idea that he wasn’t hypocritical and had never contradicted his identity.
To wrap up that comment, let’s answer this: was his death martyrdom? Not really. Jun Seo doesn’t die for Ah Jin. He dies because he cannot exist without his role in her life. That’s not noble. It’s a tragic dependency. His death wasn’t a heroic sacrifice, it’s the collapse of an identity that never learned how to want anything else.
To wrap this section up, I’d just like to say a few final things. Jun Seo wasn’t toxic because he was cruel. He was toxic because he’d mistaken suffering for love. Ah Jin wasn’t cruel because she was heartless. She was cruel because she refused to be saved. The exposure happened because he would rather destroy her image, and himself, than accept that loving her never gave him a place in her life or in her future.
Part IV— The True Beginning of Jun Seo’s Identity Crack
Moving, Exhaustion, Letters, Death, and Betrayal
One of the most interesting things about breaking these characters up is realising how some of the most overlooked scenes are actually some of the most telling moments. For example, the scene when Jun Seo overhears men talking bad about her, gets beaten, and just lays on the ground. The moment when he just… stays on the ground? That’s where his identity first cracks. And when he officially knows it. Let me explain.
Up until that point, Jun Seo’s belief system had been: loyalty gives life meaning, endurance is protection, and staying is strength. But in that scene, endurance stops being noble and becomes empty. He fights at first because that’s a reflex — Ah Jin is being violated even in absence, and that still activates him. But once he’s on the ground, something shifts. When he doesn’t get up, it’s not because he’s weak. It’s because nothing inside him is telling him to keep going anymore.
And what does his mind return to? Not rage. Not fear. Ah Jin. Specifically, their first meeting, his promise that he would never leave and finally, her words: “I need your help.” That’s devastating because it reveals the core problem: even when his sense of self is collapsing, his identity still routes back to Ah Jin needing him.
The timing is brutal for a reason. The last time he saw her, she didn’t ask how he’s been. She didn’t ask if he was okay. She asked him to help her love someone else. And he agreed. So when he’s lying on the ground afterward, replaying her saying “I need your help,” it’s not romantic. It’s confirmation. It’s the moment he realises that: this is all he is to her, this is all he knows how to be, and this will never end unless he ends it.
That scene is Jun Seo realising— not consciously, but viscerally— that staying loyal has erased him. The ground becomes symbolic. He’s already lying where he plans to end up: still, quiet, and no longer resisting.
Jun Seo’s Move: “Hi Again… Mom”
We eventually get to the point in the show when Jun Seo decides to move back into his mother’s home. This may look like it’s contradicting everything I’ve said about his relationship with her, but it’s actually psychologically consistent. At this point: his identity has already dissolved, his moral certainty is gone, and his emotional energy is depleted.
Returning to his mother wasn’t forgiveness. It was emotional regression. When people are exhausted and hollow, they often return to: familiar pain, known dynamics, and childhood environments. Not because they believe they’re good but because they require less effort to survive. It’s true that he looked calmer. But that wasn’t peace; it was resignation.
Ah Jin, Her Husband, and An Uninterested Jun Seo
Do you recall when Jae Oh rushed over to meet Jun Seo to get his help with Ah Jin and her husband. And remember how it looked like he didn’t care? Let’s break this down, because it’s brutal psychologically. Disclaimer: it’s not because he doesn’t care. It’s because he cares and has nothing left.
By the time Jae Oh begs for help, Jun Seo is spiritually exhausted. Loyalty failed. Waiting failed. Enduring failed. Protecting failed. Warning failed. Everything he believed in has failed. So his brain is in shutdown mode. Not sadness. Numbness. That’s different.
On top of that, he’s learned helplessness. “My help changes nothing.” After years of “I intervene → nothing improves” “I sacrifice → nothing changes” “I suffer → she still self destructs,” he now believes that action is pointless. I mean, why fight if it never works?
Then the fact that it’s Jae Oh that’s begging, makes everything worse. Jae Oh is still in “usefulness mode.” He’s still trying. Jun Seo sees himself in Jae Oh and it hurts. It’s like watching your past self walk into fire and knowing you can’t stop it. So he shuts down emotionally. It wasn’t “I don’t care.” It was “I can’t survive caring anymore.”
In my opinion, this is the saddest version of him. Why? Because early Jun Seo was self-sacrificing and naive but alive. Late Jun Seo was detached, clear-eyed, and empty. He’d finally learned boundaries but after losing himself. That was the cruel irony.
So does that mean he was already planning on dying?
Short answer: yes, on a psychological level. Long answer: not necessarily with a date or method— yet.
By the time he moves back in with his mother, we’re seeing passive death orientation. That usually looks like emotional flattening, reduced future planning, settling unfinished business, returning to childhood spaces, and letting go of personal possessions (photos)— aka everything we see happen. He wasn’t actively suicidal yet, but his life had already shifted into “I’m done becoming.” So when months later he makes a concrete plan, it’s not sudden— it’s the final step of a process already underway.
Goodbye Childhood Photos
We eventually reach the scenes before his death where he begins to erase himself. Starting with his childhood photos. Those photos represented a few things: the boy who made promises, the child frozen in trauma, and the self who never got to choose differently. By destroying them, he’s saying: “That version of me doesn’t get to exist anymore.” It was his way of ending the story, preventing memorialisation, and reclaiming authorship of his life.
Then we have the fact that he destroyed the photos because of his mother as well. Getting rid of the photos wasn’t about anger towards her. It was about refusing her narrative. Photos are proof of connection, of shared history. By destroying them, he’s saying: “You don’t get to keep a version of me you never truly knew.” Even in death, he denied her access. He left her with memories he chose, not ones she can reinterpret.
Jun Seo’s Letter to His Mother
When Jun Seo wrote his final letter to his mother, it wasn’t forgiveness— it was containment. He was choosing to give her something gentle so that she didn’t unravel after he was gone, even though he himself had already detached from her emotionally. That was very Jun Seo. He had always managed his pain by absorbing it quietly and redirecting it away from others.
When he said he wanted to spend his last moments giving her happy memories, it wasn’t reconciliation. It was him deciding, “I control how this ends.” He cannot forgive her nor can he understand her. So instead of trying, he steps outside the relationship entirely and turns it into a final act of caretaking. That wasn’t healing, it was resignation.
Jae Oh’s Death: The Final Breaking Point
When Jae Oh died, he broke everything. Jae Oh’s sacrifice exposed the lie Jun Seo lived by. Jun Seo believed “If I stay loyal, I prevent destruction.” but Jae Oh proved “Loving her destroys people regardless of intent.” That was intolerable. It meant that his sacrifice wasn’t protective, his endurance wasn’t noble, and his life’s purpose had failed. That collapse— not moral outrage– is what pushes him to act.
By the time he betrays Ah Jin later, it’s not a sudden moral awakening. It’s exhaustion. His belief system hasn’t changed, it’s collapsed. His betrayal was the last remaining way to separate himself from her orbit. And his death fits because Jun Seo doesn’t die fighting or fleeing. He dies having already let go. He removes himself from photos, from memory, from narrative. He leaves behind curated kindness and takes the rest with him.
Not because he wanted to die but because he no longer knew how to live without disappearing.
Revenge Plans and Betrayals
Before we do a deep dive into his death and his final acts, I want to clarify a few things. Early Jun Seo wasn’t secretly plotting to expose Ah Jin. When we see him continuously reminding her that her downfall would come, it wasn’t because he knew he’d betray her in the future. At that stage, he’s still loyal, he still believes in enduring, he thinks that staying is protecting, and he still frames himself as her shield.
So why does he keep telling her that she’d be exposed someday? Because Jun Seo lives in moral contradiction. He’s doing evil-adjacent things for her but he still believes in right and wrong. That creates cognitive dissonance.
His mind continuously thinks “I won’t stop you… but reality will.” It was his way of outsourcing judgment to the universe. By acknowledging that someone else will get her, it allowed him to stay loyal without fully betraying his conscience. Think of it as half-warning, half self-comfort. He tells her, “be careful, don’t go too far.” and to himself, he’s saying “I’m not endorsing this. I know it’s wrong” It’s moral distancing. He’s saying “I’m here but I’m not blind.”
On top of that, it’s the only power he allows himself. Jun Seo has almost no leverage over Ah Jin. He doesn’t threaten, demand, nor negotiate. This is the closest he comes to asserting anything “You’re not untouchable.” It’s a soft boundary and it’s the only one he knows how to make.
What makes all this all the more interesting is that he consciously would never be the one to expose her but subconsciously, he might have been thinking in a narrative gravity way. Not a plan though. He understood on some level that he was accumulating guilt, isolating himself, tying his fate to hers, and erasing his own future. People like that often carry a quiet sense of doom. Not: “I’ll kill myself” but “This can’t end well.” When he tells her that she’ll be exposed some day, he’s also acknowledging “if this collapses, I’ll be in the wreckage too.”
Early/middle Jun Seo’s version, before his identity collapse, that constantly warns her about her actions was in a warning state, not a threat. “This path leads to destruction. Please don’t walk it.” It was protective.
At that point, he was still thinking that she can stop, he can buffer, and they can survive this.
After his collapse, her exposure becomes destiny. After his loyalty identity dies, the meaning changes. Now, he’s thinking “My life has been for nothing.” “My suffering was pointless” and “The only meaning left is truth.” So his idea “you’ll be exposed” turns into “I will make it happen.” That’s when it officially becomes intentional. But we don’t see that fully happen until after Jae Oh’s death and Ah Jin’s marriage.
So after his collapse, his disloyalty starts to make more sense. The tragedy of the whole thing is that the disloyalty was the only disloyalty he allowed himself because he planned to disappear. In his mind, he was thinking: “I can betray the narrative as long as I don’t survive it.” That wasn’t justice. It was self-erasure as moral solution. For Jun Seo, even after his identity collapse, leaving Ah Jin behind was never an option that existed in his mind— even as he was dying.
That’s why he waits so long— he waits until he’s ready to die. Before that exposing her would’ve meant losing her, losing purpose, facing himself, and living with consequences. Jun Seo was never equipped to do that. That’s why he postpones justice until he’s ready to die. It wasn’t truth over loyalty, it was truth over existence.
To end this section off, let’s answer the question: “Did Jun Seo always know he’d die because of it?” Not specifically. He did always know that being with her was unsustainable, protecting her was self-destructive, and he had no life outside of her. That was the slow suicide. When the final plan forms, it feels “right” to him because he’d been walking towards erasure for years.
Jun Seo was not a hero who waited just like he wasn’t a villain who plotted. He was someone who knew the truth… said it out loud… and still couldn’t act on it. Not until he had nothing left.
That’s why his arc hurts. He doesn’t change his values, he just finally stops surviving.
Part V — The Car Crash: The Inevitable End
We finally reach the part in the show when all the characters meet a tragic end. From the surface level, Jun Seo’s ending seemed painfully cruel; especially when a “happy” ending for him seemed in reach just an episode or two ago. But after this whole analysis, hopefully you understand why a happy ending was never possible. Hopefully you understand that the tragic ending he got and Jae Oh got, was painfully accurate to the people they’d been forced to become since the beginning. Let’s break down Jun Seo’s final moments because it’s a lot but very telling.
The first thing to clear up is the fact that psychologically, the final car crash was disturbingly realistic. It wasn’t for drama dramatics. By the time the car crash came around, his identity was gone, his purpose was gone, his guilt was unbearable, and his love had nowhere to go. So when he drives them off the road, it’s a final attempt at fusion, punishment and protection combined, and “If I can’t save you, I’ll end us both.” That was an annihilative attachment.
This can happen in real cases of extreme trauma bonding, obsessive relational identity, and chronic guilt and despair. The drama may have exaggerated the spectacle, but the psychology was accurate.
Then we get to the line “let’s go to hell together.” That line wasn’t romantic bravado, it was a confession. By the time he says that, Jun Seo already knows two things: He cannot live with Ah Jin. And he cannot live without Ah Jin. Those aren’t opposites for him, they’re the same conclusion.
Taking her hand was instinctual. Holding her is how he had always regulated fear, guilt, and meaning. When he says “let’s go to hell together,” he’s not damning her. He’s acknowledging that, in his mind, their fates were fused long ago. Hell wasn’t punishment, it was proximity. It was simple wherever they are together when the world stops asking him to endure.
This then leads us to him crying in the final moments. This is the moment that breaks the fantasy. He’s not crying because he’s scared to die. He’s crying because this is the first time he’s actively choosing something that will hurt her and that contradicts the core of who he believes himself to be. Jun Seo’s identity has always been: protect, stay, and absorb pain. Driving off the road violates all three and he knows it. That’s why he looks at her. That’s why he cries. It’s grief for the self he’s destroying in order to finally escape it.
The crash eventually happens and we see Jun Seo try to stop her from getting out of the car. This is incredibly telling and it’s not cruelty. In his final moments, Jun Seo was acting on a belief that has governed his entire life: “separation is worse than death.” Letting Ah Jin leave the car would’ve meant she survives, he dies alone, and their bond finally breaks. That is the one outcome his psyche couldn’t tolerate.
To him, her trying to escape isn’t about survival, it’s abandonment. Not in a manipulative sense, but in a deeply disordered attachment sense. His last act wasn’t about trapping her. It was about preserving meaning at the only scale he understood: together or nothing. He didn’t stop her because he wanted her to suffer. He stopped her because if she leaves, his life ends having meant nothing to the one person it revolved around.
Jun Seo didn’t take Ah Jin with him out of hatred, vengeance, or control. He did it because his loyalty replaced his identity, his love fused with self-erasure, and him dying with her felt less terrifying than dying without her. That’s why the whole scene is so painful. Not because it’s dramatic but because it’s honest to who he’s always been. He doesn’t choose death. He chooses not to be left behind; even if the cost is everything.
To end this off, let’s answer the tough question: Who was Jun Seo? Jun Seo wasn’t obsessed because he loved too much. He was obsessed because his identity was formed through trauma, his loyalty replaced morality, his self-worth depended on endurance, and his exit strategy was always disappearance. He didn’t need to be with Ah Jin. He needed her suffering to mean something.
When that meaning collapsed, so did he.
Part VI — Why People Romanticise Jun Seo (And Why They Shouldn’t)
If there is one comment I see the most under edits of him, it’s “I want a man like him.” And let’s be clear, this isn’t me shaming you. Before I did a deep dive into Jun Seo, I was right there with everyone. And who can blame us? Fiction often frames this kind of attachment as “pure,” “safe,” or “ideal,” especially because he never hurts her, he never demands anything, he never centres himself, and he’d die before betraying her.
On the surface, that looks like a dream. But psychologically, this is not a healthy partner. And here’s why:
His Loyalty Isn’t Chosen — It’s Compulsory
Jun Seo wasn’t loyal because he wanted to be. He was loyal because leaving felt like death, identity collapse is terrifying, and he doesn’t know who he is without her. That means his “choice” isn’t free, his devotion isn’t flexible, and his love isn’t rooted in autonomy. A partner who cannot leave is not safe. No matter how gentle they are.
It’s important to remember that characters like him are fictional no matter how realistic the psychology is. If you want to see how Jun Seo would eventually turn out, look at the horror movies/dramas of male characters who don’t even let their partners to leave the house, who beat them, and never leave no matter what. The best way I can describe what he would be like in real life is the character in episode 1-2 of Judge from Hell. I’ll say it again: a partner who cannot leave is not safe.
He Cannot Tolerate Change in the Relationship
If Ah Jin became healthier, Jun Seo wouldn’t know how to meet her there. Why? Because his role depends on her being broken. His identity is built on protecting suffering. Her healing would make him unnecessary. That creates an unconscious pressure of: she can’t fully heal or he disappears. That’s not intentional control but it is relational stagnation.
So if Ah Jin healed and genuinely didn’t need Jun Seo anymore, for Jun Seo, that would be identity collapse. His attachment to Ah Jin wasn’t just love or loyalty— it was role-based. He survived by being necessary. Protection wasn’t something he did; it’s who he was. If Ah Jin healed quietly, without confrontation, without asking, without needing rescue, Jun Seo wouldn’t feel relieved. He would feel erased. Here’s the important part: He wouldn’t accuse her. He wouldn’t rage. He wouldn’t demand she stay. He would internalise it as: “I failed.” “I was never needed.” “I misunderstood everything.” and that’s far more dangerous than anger.
That would eventually lead to Jun Seo sabotaging it. Jun Seo wouldn’t “create problems” in the dramatic sense but he would gravitate toward situations where he could still protect, endure, or sacrifice. He would never just be happy. If she suffers, he’ll endure her pain and feel guilty for not protecting her enough. And if she heals, he’d feel horrible too. There is no winning for a guy like Jun Seo.
If Ah Jin became emotionally regulated and self-sufficient, Jun Seo would feel unmoored. And for people like Jun Seo, that would lead to overinterpreting threats, seeing danger where there isn’t any, and attaching meaning to suffering. Which would eventually lead to abuse.
He may not want her hurt but he needs a word where hurt still exists, because that’s the only world where he knows how to function. A healthy Ah Jin would unintentionally confront him with the question he cannot answer: “Who are you if I’m okay?” That question alone could destroy him.
He Sacrifices Instead of Communicating
Jun Seo doesn’t know how to ask for reassurance. He doesn’t know how to set emotional boundaries. He doesn’t know how to clearly express his needs, his fears, or his limits. Instead, he absorbs pain silently and reframes suffering as virtue. For him, endurance becomes proof of love. The more he hurts quietly, the more loyal he believes himself to be. But this kind of emotional self-erasure does not create intimacy. It creates resentment, moral distortion, and eventually collapse. When someone never voices their needs, those needs do not disappear. They turn into quiet bitterness, emotional numbness, and sudden catastrophic decisions when the internal pressure becomes unbearable. That is exactly what we see later in Jun Seo’s story. Healthy relationships require mutual visibility, mutual vulnerability, and honest communication. Silent endurance only delays the damage.
He Replaces Morality With Devotion
This is the most dangerous shift in Jun Seo’s psychology. He does not ask himself, “Is this right?” He asks, “Is this loyal?” Loyalty becomes his sole moral compass. Once that happens, harm can be justified, truth can be postponed, and accountability can be sacrificed as long as it serves devotion. When loyalty replaces ethics, anything can be rationalised. Protecting someone becomes more important than protecting innocent people. Staying faithful becomes more important than being honest. Enduring becomes more important than doing the right thing. A partner who prioritises devotion over morality will eventually enable destruction, whether that destruction harms others, themselves, or both. Jun Seo does not intend to become dangerous. But his belief system makes harm possible.
The Uncomfortable Truth: “Why Does It Feel Safe Anyway?”
People are drawn to characters like Jun Seo because he feels emotionally predictable. He will not abandon. He will not betray. He will not compete for power. He will not assert himself over you. He orbits. He adapts. He stays. That kind of consistency can feel incredibly comforting, especially for people who have experienced instability, neglect, or betrayal. But safety without autonomy is not real security. It is containment. A relationship where one person cannot leave is not built on trust. It is built on dependency. Healthy relationships come from choice, boundaries, selfhood, and the knowledge that both people are capable of walking away and still choose to stay. Jun Seo never truly had that choice.
None of this means that Jun Seo is evil, manipulative, or intentionally toxic. His love is real. His devotion is genuine. His gentleness is sincere. His selflessness is not an act. But his attachment is tragic, not aspirational. You can write him as deeply loving, profoundly loyal, and emotionally sincere without framing him as someone anyone should want to emulate or be loved by in real life. His psychology is moving because it is broken, not because it is ideal.
Jun Seo is not a fantasy partner. He is a warning wrapped in devotion.
Part VII — What If?
To wrap up Yun Jun Seo’s analysis, I had to include a “what if” section because his entire story feels like it exists inside that question. So we reach the biggest one of all: if Jun Seo never met Ah Jin, would things have been better?
The answer is… different, yes. But better? Only conditionally.
Jun Seo was already shaped long before Ah Jin entered his life. He grew up with an emotionally exploitative mother, in a world where love meant obligation, endurance, and quiet sacrifice. He learned early that his value came from fixing, absorbing, and staying. Ah Jin didn’t create that structure. She activated it. She gave it somewhere to go, someone to attach to, and a story to live inside.
Without her, that pattern doesn’t disappear.
It redirects.
Jun Seo would have likely attached himself to someone else who felt wounded, distant, or in need of saving. He would have become a quiet enabler in a different relationship, or lived a “functional” life where everything looked stable on the outside but felt hollow underneath. The specifics would change, but the emotional pattern would remain intact.
Same song. Different font.
So yes, without Ah Jin, Jun Seo might have survived. He might have built a career, maintained relationships, and lived a life that others would describe as respectable or even admirable. But internally, he would still be emotionally repressed and deeply lonely. He would still be the person everyone relies on but no one truly understands. He would still struggle with autonomy, with setting boundaries, and with the quiet, aching desire to be chosen—not for what he provides, but for who he is.
Another uncomfortable question is this: what if someone healthy had entered his life instead? Someone emotionally stable, communicative, and capable of loving him without needing to be saved. On the surface, that sounds like the “solution.” But for Jun Seo, that kind of relationship would feel unfamiliar, even destabilising. He would not know how to function in a dynamic where he isn’t needed, where love isn’t proven through suffering, and where presence doesn’t require self-erasure. Instead of healing him immediately, it would likely trigger confusion, insecurity, and a deep sense of inadequacy. He wouldn’t feel relieved. He would feel exposed.
And if that relationship continued, one of two things would happen: either he would slowly learn to redefine himself outside of sacrifice—which would require an identity-level transformation he was never equipped for—or he would unconsciously pull away, gravitate back toward dysfunction, or recreate situations where he could return to the only role he understands.
Because the truth is, Jun Seo doesn’t just love people.
He needs to be needed.
That is the core of his attachment.
So even in a completely different life, even in a softer version of his story, that need would still shape his choices, his relationships, and his sense of self.
Ah Jin didn’t give him his wound.
She gave it a name.
Final Thoughts
Yun Jun Seo’s story was never about love in its purest form.
It was about what happens when love becomes identity.
When loyalty replaces morality.
And when a person slowly disappears in the process of trying to make someone else’s pain meaningful.
Every choice he made, every line he crossed, and every part of himself he erased followed the same internal logic: stay, endure, protect.
Not because it was right, but because it was the only way he knew how to exist. That’s why his story doesn’t feel like a sudden tragedy. It feels inevitable. He didn’t fall apart at the end, he was unraveling the entire time, just quietly enough that it looked like devotion.
What makes Jun Seo so compelling isn’t that he loved deeply, but that he never learned how to exist outside of that love. He wasn’t choosing her freely—he was built around her. And when that foundation finally collapsed, there was nothing left to hold him up.
That’s why his story hurts the way it does.
Not because he lost her, but because he lost himself long before that moment ever came. He didn’t die because he loved her too much.
He disappeared because he never learned how to be anything else.
And that’s a wrap! Hello again! It’s been a while since I’ve posted and I’ve missed you and posting. I’ve been super busy so I still can’t post weekly but I will continue to post when I can.
Next time I post, we’ll deep dive into Kim Jae Oh and then say a sad goodbye to Dear X and its characters before moving on for good. I already have a movie lined up to review and I’m excited to get into it.
I really hope these give you a better idea of the characters and it’s understandable. It’s a long read but it really lays everything out for you.
If you want to watch Dear X, you can find it on Viki and Disney+!
I’ll be back and I hope to see you soon!
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