I havent read the novel so i dont know for sure but from what i think is he became a psycho after getting his memories back because he was always a psycho, that just who he was and still is, when you loose yoire memories or dont know who you are or what you should act like , hes only like this because of yeon but when he remembers he remembers why hes the way he is and how much he liked killing
Idk if i explained it well sorry, i could be wrong but thats just what i think

please someone spoil me why chaewo become total psycho after gaining his memory back. I stopped reading the novel weheheh