But he also didn't want to give him a blowjob because he might say something mean like "doing this to a man is disgusting". There's other evidence too, like when they did it on the porch he would only do Bum from behind and got mad when Bum turned around because he had to look at a man's face. Sangwoo is using Bum as a substitute for his mother and anything manly about Bum (like a penis) disrupts that fantasy. Anyway this is just my take on things he is super drunk so I do think that he threw up because of that, but he definitely is more attracted to Bum's feminine side.
okay I think that Sangwoo is using Bum when it comes to the comfort he feels like having his mom back. but I think that Sangwoo only wanted to be loved by his mom and their talk that apparently, his mom raped him or sexually abused him which could be why Sangwoo killed her because he found her disgusting. It's true that Sangwoo was straight, to begin with, but when it comes to Bum I don't think he has been disgusted with him from what I've seen. when they had sex and entered the house, sangwoo had bum facing him where he could see everything and he looked like Sangwoo was enjoying it to me. And when it came to the blowjob and Sangwoo not wanting to do that it just seemed like Sangwoo was not ready at the time and need more time to think about doing something like that. Bum was kind of pushing it trying to be in control and I don't think Sangwoo liked that which is why he took over in the end, having bum summit to him. Well anyway, this is just how i saw this situation.
Okay, so I don't understand why ppl keep saying that Sangwoo is disgusted with Bum just because he threw up one time. I think Sangwoo threw up because he was very much drunk and had to much to drink. That's why he did a lot of reckless things this episode. like for example letting Bum drive and talking about a murder he committed in public. Sangwoo was the one who mentioned about having sex with Bum and getting all touchy feely with him. So I don't think he was disgusted at all with Bum. Sangwoo has even kissed Bum when his breath smelled of throw up and he wasn't disgusted by that and this happened in the first season if some of y'all can't recall that scene. anyway I don't think he dislikes being intimate with Bum or else he would be the one making the first move in the first place