Imo they should've broken up if they weren't compatible,now it's a whole mess ┑(￣Д ￣)┍
Relationship isn't like that, sometimes you like so much the other person that even when something that he/she does don't make you happy (and I'm talking about choices), you still want to try understand and stay in the relationship because of the love. And I don't think we need to be compatible with anyone, we need to be a plus in each others lives. Everyone is complete as individuals.
However everyone has a point of view and I respect yours.
The problem here isn't about how unfaithful Shinwoo is (and of course this is wrong in every possible way), but how many times Shinwoo asked Sebin if he liked the S&M play and he said yes? Man, you can't say you like this type of thing only because your partner is into. Analise all the pros and cons first then answer. In my opinion it's what made Shinwoo angry.