Actually, he will get better. He won't change his nature of course but he'll change his behavior, something he is very capable of doing(like every person with ASPD). He'll realize that he is the one who has to adapt if he wants to maintain their relationship, not Inseob
I mean, I have read it and he does change but it's not to the extent that ever really feels... safe? Like, he technically treats Peter better but it's not in a way that even attempts to redeem him. Also the bar is set really lox for him so...
Never stated that anything will ever redeem him or that he'll ever be a completely safe option , just that he will get better by changing his behavior.
When the character is a literal psychopath, they never "get better". There is no redemption arc. Just acceptance of one's fate. Peter will be in mental shackles for life. And if he ever breaks out of them, Wooyeon will put him in real ones.