Hm, from the stress of keeping the plagiarism secret coupled with their toxic treatment of each other, I think that relationship wouldn't have lasted that much longer, even without Youngwon's intervention. I mean, if they'd had moments where the gf said sorry, begging forgiveness and promising "not to do it ever again", like violent husbands do with their wives, then maybe they could've kept it up quite a while. But, with the way she was absolutely detached and zero invested in "making up" after each time they "argued", not even apologizing for the sake of "appearances", I don't think the guy would've been able to keep delluding himself for much longer.
Maybe you're right, but she affected him a lot, even now he can not forget her... As much as the relationship had been toxic I don't see them ending just because of this. He needed a stronger reason to see who really was his girlfriend... I think after the cheating he saw that there was no solution to their relationship.
I don't know... Kihyun knew that his girlfriend was copying his paintings, but he still continued with her because he loved her very much. If it was not for Youngwon she would continue to suck everything out of Kihyun... In the end he kind of helped to end this toxic relationship and showed that she was a damn bitch... But I don't agree with what he did, he hurt Kihyun so much!!! Kihyun can't move on because of what happened... I'm sad and confused ╮(￣▽￣)╭