Responses
It depends on the person. You can't generalize people that way. Besides, a physical reaction is a physical reaction. If a hole feels tight, it would feel good regardless of who's fucking who. For example, someone gets raped by the same sex. Your body reacts to sexual pleasure regardless of your attraction towards them.
Sangwoo's not in the right mind anyway, author's words. He's a confirmed hetero, he saw his mom in Bum when they fucked but somewhere towards the end he felt something for him, romantic or otherwise.
I really doubt sangwoo is Heterosexual if he was enjoying sex with bum. I just think this is another case of misunderstanding how Sexualities work because its shunned in Asia alot. Idk just my take.