Briefly, Yule was a psychopath among other stuffy since he had a tendency to break things (see ch.69). In his mind, he thought that if he broke things by his own actions before he lost them, he'd feel less pain associated with what he lost (eg. his mum). His mother and then later, Kyung Soo, were prolly the only two people precious to Yule.
As for him orchestrating the gang rape (asking his friends to rape Kyung Soo), he wanted to break Kyung Soo 'cause he was starting to grow attached to Kyung Soo.
The ironic thing of this whole story is Yule had what he lost (Kyung Soo's love for him) and now he's trying to reclaim it, if that makes sense.
Kyung Soo initially and genuinely loved Yule, but since Yule was afraid of attachment and losing Kyung Soo, he decided to break Kyung Soo...only to realize that he DID love Kyung Soo. So the story ends with Yule trying to reclaim Kyung Soo's love for him.
I still don't understand why Yule asked his friends to rape kyung. Is it really Bcuz he was a psychopath?