
lol dude, Im sorry to break it to you but there is not a reality in which that happens. He doesn't care about Bum. To him Bum is a plaything to abuse and take out his frustrations and mother complex. Bum is an object to torture and torment, thats what he enjoys. It could be anyone, it doesn't have to be Bum. Bum is just well suited as he is weak and easy for Sangwoo to control. Sangwoo will always act crazy to Bum because he is crazy. He's so far gone that there probably isn't a therapist or psychologist alive that could rehabilitate Sangwoo.

Yeah, there is no cure for that type of sick. Give him drugs, and he'll be a sick bastard on drugs. Have him talk, and he'll tell you pretty stories and try to manipulate you. You can try extreme behavioral therapies but you risk being inhumane and still not getting anywhere. Just because it is sick does not mean we can cure it.
I wish there could just be a happy ending or that at least sangwoo could stop acting crazy towards bum. when he grabbed his thigh he looked like he was so mesmerized but it never really seems like a gentle or caring touch I just want them to get it together.