Responses
Actually it makes total sense. Sangwoo is not attracted to men. He's attracted to Bum because he reminds him of his mother and because he does everything he says. He's unquestionably loyal to SW and completely obsessed with him. That's why he likes Bum. He gives him the unconditional love that his mother should've given him.
Yes, he prefers to kill women, but many serial killers feels attracted to their victims in a way, since they're often in part sexually motivated.
If Bum was a woman, he'd be in resting in 10 pieces by now.
But... yeah. Sangwoo: Bum, I'm not gay.
If you say so, Sangwoo.... if you say so....