It's their old tutor. The black one and pruple haired one kinda grew up together and had one tutor together and the purple haired one was in love (kinda obssessed) with him and later on it's revealed that the purple haired one was clinging to mc because he looked like his tutor and there will be misunderstanding with the mc and ml because mc started to think that the ml only liked him because he looks like him but that's not true.

But he gets abused at home by his father. His sister said to Jun that Yohan lives the best life but that's a lie. I don't know if she doesn't know that he's getting abused or just chose to not acknowledge it but yeah. And he gets excluded by his family though that's not an excuse to get angry at somebody to the point of sexually assaulting them etc. But it's understandable that he gets angry at Jun since Jun insisted to eat together but not to such a point. And I think he lied about some things about himself like his favourite food or smth but I'm not sure about that.

I don't remember much but later on jun will get bullied in school because of yohan and his mental health will get down but later on when they got into the same university, Yohan kinda became devoted to jun (like I don't how to explain) and yeah after some time they get together (they both freaky) (sorry for the sloppy explanation but it's been several months since I read the novel)

He basically used mc because he looks like his first love. He doesn't see mc for who he is but as his first love (yesong or whatever his name was) and when mc confronted him and rejected him and said he's not his first love, he started to get physhical and literally attacked mc (even throwing him onto a road, choking him etc.)

I don't remember much but Jun became bully victim in class after what Yohan did and Yohan didn't do anything about it and I'm not so sure if Yohan kinda ochestrated it or not but he didn't do anything to stop this bullying, I guess because he wanted revenge or smth (I'm sorry if my explaination is plain and not good but I don't remember much since it was many months ago when I read it but I remember I didn't like these chapters at all and felt sorry for Jun but at the same time I was like: He also didn't do anything and was ignorant when it came to bullying others)