I thought he was just a jerk with trust issue, but he's actually a psychopath.. now I feel...

Well, sociopath is the correct term, since he can actually live in society (I mean, he didn't kill anyone before the apocalypse so... )

If we want to go by the correct term then it's psychopath. Sociopath is not recognised in modern psychology anymore and how we think of sociopath is actually anti-social personality disorder now. Moreover, it is believed (but still in debate as well) that there are varying degrees and traits of psychopath, so they can manifest differently in each person.

Psychopathy doesn't mean anti-social behaviour, but mainly refer to the lack of empathy and limited prosocial emotions. Although there may be some overlaps (e.g. lack of remorse or guilt, impulsive), but just like you said, he was on his best behaviour before the apocalypse, so I don't think he has APD.

TLDR; sociopathy is outdated and it's actually anti-social personality disorder. Psychopathy is actually what I'm looking for here with his lack of empathy and all.

I'm pretty sure psychopathy and sociopathy are both under anti social personality disorder. Either way, there's nothing to feel bad for because his family understands him, so does Soojeong and it's not like he's incapable of feeling emotions or anything. He cares for his sister's and for SooJeong

Oh wait I just realised what you meant, yeah his sisters are great

Don't wanna be like "well aschually" here, but to be clear, I used psychopathy because I wanted to mention how he lacks empathy naturally. (And personally, I don't think he has most anti-social personality disorder traits. Only some overlaps from psychopathy traits.) And yes, I LOVE his sisters so much ToT

its aspd, anti social personality disorder, not psychopathy or sociopathy. also possible he has an extreme case of alexthymia since i do think he genuinely love soojeong whereas if he had aspd hed likely view soojeong as more of an object to own than an individual

psychopathy is a term that technically fits under aspd whatre you on

I get that.. my bad for using "psychopath". I want to just use the pop term and leave it at that. Tho psychopathy and aspd are not mutually inclusive.. Anyway, I didn't wanna get technical because I'm no expert and this topic is still in debate in the scientific world. My point is he seems to have tendencies/nature similar to that of psychopathy. And personally, before the whole apocalypse thing, he doesn't seem to have aspd..

HONESTLY, I DIDN'T WANT TO DIAGNOSE HIM WITH WHATSOEVER. I just want to highlight his natural inability to understand so-called normal emotions. He's definitely not neurotypical and that's it. THAT'S IT. I'm sorry for using a pop term for a quick comment. :/