I wouldn't go as far as to diagnose him, but he did go through very traumatic experiences stretching from childhood to his current age. I think it's safe to say that even when he knows his behavior is self-destructive and harms others, he does them repeatedly because they're familiar and that's what works. The author does give him character development though. Sorry this went too long ಥ‿ಥ
Ok, I'm just like what? he wants Dayeol so bad but he still doesn't like him.
He does like him but I think at some point near the end he says that he’s scared of liking him and whit it might do to them, so he kind of ignores his own feelings for a while and try’s to repress them, but the feelings eventually do get acknowledged at the end.
I know authors likes to make their stories different and unique but I dont understand whats going on in taeyuns head. Is he bipolar?