I like your theory, except for the fact that although the English translation is "Unchanged man", the original Korean title is "Yuwon unchanged", implying that it's Yuwon who can't move on from the past
I really think Yuwon has some kind of psychotic break where he's actually the one that killed all those people in the past and Dohun took the blame. Yuwon then repressed everything and blamed everything on Dohun.
I feel like the narrative has been hinting at the fact that Yuwon is an extremely unreliable narrator since the start of Dohuns POV in season 2. In s1 Yuwon blames Dohun for manipulating the landlord into kicking him out so they can live together. In s2 we find out Dohun is innocent. In s1 Yuwon is sure Dohun killed Seongwon, but in s2 we just found out Dohun held back.
I'm super curious what will happen when Dohun watches Yuwon on tape in the next chapter like Seongwon suggested. My theory is that we're gonna see something that indicates psychological problems, like staring vacantly into space or muttering to himself...
Ofc I'm not saying Dohun is some innocent smol bean or something, he's also plenty fucked up XD I'm also not excusing what Dohun did at the end of s1. BUT I think that Yuwon is way more fucked up than we think and it's gonna be revealed soon
Anyway I love this story so much, the author is a genius making us readers theorize like this
I think the Seongmin saying “You really don’t know anything about Jeong Yuwon and how you’re supposed to treat someone you love” is the most important quote that puts all of Dohun’s struggles in a single sentence.
All that Dohun wants is to take away all of Yuwon’s pain and grant him happiness, but it’s just as broad as like making a wish but not setting it into motion, or in Dohun’s case, going about it in the wrong way. He cannot understand that people are prone to change and that possibly Yuwon himself had changed a long time ago. So he clings to the old ideals of their childhood (buying a whole pension, giving Yuwon branded clothes) not understanding that those were things Yuwon wanted so that the two of them—young, broke kids with no family dependent on each other for survival—could lead a happier life together.
Now that Dohun has the financial stability, he’s dead set in his beliefs that it’s enough for them to become “happier” but that in itself is childish and idealistic. Throughout the entire story, Dohun’s the one who’s unchanged. Yuwon’s changed self leaves Dohun to a completely new slate that he doesn’t know how to navigate. He may love Yuwon but he does not know the way to make Yuwon happy now, and he probably never will because Dohun’s the unchanged man and that’s why I believe the two of them, now on differing paths, will never achieve the true perfect happiness they always dreamt of.
In my personal belief, I think that Yuwon does love Dohun in his own way because if not, he would’ve walked out a long time ago. But he cannot accept that Dohun cannot give him the normalcy that he desires, after everything he’s been through. Yuwon just “wants to be able to breathe” freely, like he said how he felt around Seongmin (but that isn’t an admittance of love). And instead of slowly introducing him to the idea of a relationship, Dohun completely smashes all the baby steps and jumps straight into the boiling pot, so yes Dohun, you fucked up right from the start