cause he is a sadist ლ(´ڡ`ლ)
No he's not. Sadists are entirely consensual and it is the M who leads. T. This is nothing more than abuse.
Maybe it's a "I like to bully the one i like" type of thing
this^. He sexually assaulted and raped Jinwoo. He was too traumatized by it to fuck his gf... Sangtae says it himself he has an "obsession", it has moved from an innocent love to terrorizing Jinwoo because he'd rather Jinwoo hate him and be in his life than not be in it at all.
He is a sadist and has internalized feelings.
so seme always loved him? then why he so mean to hem before in the work?