guys nothing happened per se, we're still in the flashbacks at chapter 84 i made the comment because is just my understanding of the situation with all the context we're getting from them so far.
in chapter 84, yoowon and duhon are talking, and when duhon notices yoowon is on the phone with seongmin, planning to go eat with him, he gets annoyed and says "don't go. you don't need to see him. there's nothing good for you in that person."
then he tries to tell yoowon what seongmin did because he wants him to understand that trusting people who aren't him is absurd. he wonders, "how would you react when you find out the truth? what expression are you going to have this time?" and asks him, "aren't you going to feel betrayed? much more than what you felt with me?"
but then dohun thinks "i wanted you to show a look of relief upon learning the truth, but what i saw wasn't a face consumed by anger and a sense of betrayal, it was an expression i didn't even know how to begin to describe."
yoowon insists seongmin isn't a bad person, and eventually tells duhon he's not going out to eat with him anymore just to calm him down. later, when they're in bed, duhon asks if he's being bullied or harassed at work, yuwoon says no, then dohun asks, “you don't bang your head against the wall anymore, do you?” but yoowon doesn't answer.
then the chapter ends with duhon asking him, "are you happy that we've found each other again? do you like having me by your side, in our home? i do, i like that we've found each other again, and that you're by my side. you feel the same way i do, don't you?" supposedly yoowon is asleep through all of this, so duhon says "yeah" to himself, almost as if he's imagining yoowon saying it back to him.
so yeah, yoowon clearly considers seongmin a very dear friend and treats him much more warmly than he treats duhon, and you can really feel how much that hurts duhon. he's starting to realize that what he's doing isn't actually making yoowon happy, and i think that's why we're seeing him question himself more and more. the more i read, the clearer it becomes that neither of them is ever going to be truly happy like this, i just need us to get back to the present already because i NEED to know where all of this is going

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they're so doomed bro