Responses
But she could be born a psycho
As far as I've noticed, she never showed any psychopathic tendencies, she displayed various emotions, she felt guilty for the things that happened to hear friend and that guy she used to like. But it could be that she's developed sociopathic behaviors to cope with her situation, and now suffering from separation anxiety. Just a guess though.
Guys, let's not forget Siyun actually used to be a very charismatic guy before the accident which left him feeling all alone. He wanted to be loved by everyone, so when he became alone, he became obsessed with the only person who loved him and did everything he could to keep her to himself. But now that he's healing, he's coming out of the dark part of him life and going back to his past charismatic, happy self. He's not a born psychopath.