"I'm not gay" .... But didn't you.. and... Okay now

Sangwoo isn't gay. It's just a fact. Yes, he's had sex with Bum and is obviously attached to him. But that's all because of Sangwoo's PTSD and psychological problems. His attachment to Bum isn't because he loves or truly cares about him. Bum resembles Sangwoo's mom. Why he loved and is so attached to the memory of his mom, I really have no clue.