Exactly...Yura stopped because he likes another girl (Moa). And Moa continued with his brother because she likes him? 
1+1= 2 y'all. I understand that we feel bad for Yura but don't put all the blame on Moa. Yura could of walked away and he didn't and he is now probably gonna be hurt by Moa again. He knows that she sees them only as s** buddies and yet continues to let her spit on his feelings. Like he is a grown man?! Moa isn't a player she didn't mean for this to happen. She didn't know they were brothers. She would be a player if she knew and said yeah I'm gonna have s*x with both of them for the fun of it. And his brother?! Like come on Moa isn't the villain y'all are painting her to be. Yura is letting shi*** things happen to him. Moa isn't thinking about his feelings and wanted to stay friends. And Yujin is a horn dog that doesn't care about his brothers feeling either. 
I must become strong..