I think Yule likely has borderline personality disorder with core psychopathic traits. He was traumatized by his mother’s death and growing up, everyone ostracized/blamed him for it. So yeah, his developed concept of receiving and giving love was broken. He has a tendency to destroy things/relationships whenever he is aware of their significance to him. He lost his mother whom he grew very attached to, so with his reasoning, he would rather destroy something precious to him before he loses it likely to avoid pain from the loss. My guess is that he started to grow attached to Kyung Soo or that he was starting to have feelings for him, so out of fear of losing him, decided to break Kyung Soo and drive him away with the gang rape. That or, he orchestrated the gang rape to test Kyung Soo’s love for him and plainly to see if he could do it. I think his borderline tendencies make him unstable and obsessive with Kyung Soo in a way that he always feel “empty” or like an empty being that requires Kyung Soo to fill his sense of self. He has an intense fear of Kyung Soo abandoning him, so he went through whatever means (rape, manipulation/blackmail) to chain or make Kyung Soo stay with him.
I think borderline and psychopathic traits complement each other, but do share one similarity: emotional dysregulation and Yule is a model example of that with his impulsivity and pretty much solving things with rape and manipulation/blackmail. Of course, the author prolly just made Yule as evil as you could get without actually giving him a specific mental illness...
But I think pretty much, Yule is like: I fear growing attached to someone/something and if that gets taken away from me, I rather destroy it first than lose it later on to avoid the pain that would come with that loss. Then after that someone/something precious to me is gone, fear of abandonment comes in and I need to do everything I can to get back and tie that person/thing to me. Like a yo-yo, back and forth.
Sorry for the long response, Yule is essentially a psychopathic ass, haha (⌒▽⌒).
wow :))) I was thinking the same thing, well, sort of :'> nice explanation btw <3
Cuz he had it aince he was small child , for child of that age to have mental illness that sever it not normal specially when it seem his house was not abusive , his mother seem like loving mam so what caused his mental illness . . Also the sister kind pissed me of just cuz you care about your brother doesn't mean you interfer with his love life like that , so annoying .