
I don't think Bum has every questioned why he was attracted to Sangwoo. He liked the affection Sangwoo gave him and is trying to convince him self that he did not love him. He thought of the affection Sangwoo gave him and was constantly telling himself it was not love he felt in those moments. The thought process Bum had in 15 is very contrasting the thought process Bum had back in chapter 1 where he'd constantly justify his own actions "because of love" even when those he obsessed over got hostile. Bum was having an internal conflict between how he felt about the idolized Sangwoo he obsessed over and the real Sangwoo who has abused him. He was so torn between his feelings and I don't think he was as able to fully convince himself that he no longer loved him.
But doesn't Bum not love Sangwoo anymore?