
I actually really wanted Sangwoo to go to a mental institution where he could get the help he needs, and I wanted Bum to go into therapy and find a healthy, happy love life where he's treated perfectly and his partner understands his trauma and doesn't rush him into anything and doesn't make him feel bad, but I figured it wasn't going to happen. I really wanted it to end with Bum happy, and Sangwoo getting the help he needs, but I figured it wouldn't happen.

I'm not saying he could've lived a happy life after that. He would've spent the rest of his life in an institution for the criminally insane, where he could've been treated for his PTSD and psychopathy, and also possible schizophrenia. Bum needed it too, I know that, but Sangwoo always gets overlooked because he was a bad guy. But all bad guys can be cured, it just takes time and patience and the right doctors and medications. Sangwoo would never be able to set foot outside the institution ever again, and it's likely Bum would've ended up in there for at least a decade for PTSD, depression, borderline personality disorder, and possible schizophrenia.

Even though you say he could be treated but it would require spending the rest of his life in a mental institution. That doesn't sound like actually treating something. For me, it's basically that he's untreatable but because of that he must be in a mental hospital. Though Bum would really need something like that since he didn't seem so fucked up. (But regarding Sangwoo, I don't think he has an inborn psychopathy, in the "kid flashbacks" he seemed rather normal and was just gradually fucking up, so then he might be somehow treatable. I don't even think that he's a psychopath, but more of a sociopath. My note was basically just about psychopathy which is untreatable, unless the psychopath himself wants to do something about it, which is rather rare.)
or the BeAuTIfuL LiE