Obviously, I am not a psychiatrist but I think Yule has borderline personality disorder with core psychopathic traits, developed from the trauma of his mum’s death and being ostracized for it. You’re on the mark, Yule is like: I fear growing attached to someone and if they get taken away from me, I rather destroy it first than lose it later on to avoid the pain that would come with that loss. In essence, he is trying to detach himself from that person. Then after that someone precious to him is gone, fear of abandonment comes in and he needs to do everything he could to get back and tie that person to him (blackmail, rape, imprisionment, manipulation, etc). Like a yo-yo, back and forth.
Yule is well, self-destructive with his relationship with Kyungsoo, reckless sex, impulsive, fear of Kyungsoo leaving, etc. But he also lacks empathy so...yeah, psychopathic too.
Yeah, I like the way you explain. Much better than me in many ways. Yeah, it really might have started from that incedent with his mother.
I think the reason why his acting that way to approach Kyungsoo might be because he's too desperate to have him back and he doesn't know how to show his feeling for him properly. IDK, whatever I'm saying is just my rambling thoughts.
I think he needs to see a Psychiatrist. With his obsessive and dependent tendency towards Kyungsoo. Maybe it all comes back to his family. I don't think he grew up in a loving family (not that there is an emphasis on that) so he might not be familiar with affection and he didn't know how to handle and show it properly. Or maybe just like he said about his mother maybe he is afraid that one day suddenly Kyungsoo will leave him so before that happens he break him?