Exactly my thoughts. Sungho wanted to desperately be with Dohyun, which did not give him much choice in the matter. But it's his set mentality that didn't give him a choice, not Dohyun, as assholish as the whole situation was, at the end of the day, it was Sungho who decided it. Dohyun just knew how dependent Sungho is on him and used it to his advantage.
Sungho chose to go along with Dohyun's conditions. That makes Sungho responsible for his actions. He said yes instead of no. Everyone who is blaming Dohyun is WRONG: there is no justification (so far) for what is done here. But I don't doubt there's some insanity at work.
In the flashbacks Dohyun gave Sungho a choice. Either they fuck or they won't be friends anymore. Sungho chose to fuck because he didn't want to loose his only friend. It was NOT rape. Is Dohyun an asshole? YES, but no one deserves to be kidnapped, abused, and raped everyday.