Well seju did cheat, she have sex with a man and sumin find it out. It's a bad timing cuz her parents just died and she still doesn't recover from that. I think it's better that she end up with sujin. And seju with the hot swimmer girl. They find peace. That's all matter. Sometimes there's thing that looks good together but doesn't fit in to be together.
I know that kick in the breast area hurts a lot! That jerk deserves death.