Bum is already attached to Sangwoo because he acted kindly sometimes and Bum doesn't want any help now. Even though he can exonerate himself he still wants the murderer
Well, if he hadn't killed Ji Eun, I'd think that way too... But I think Bum is in a way using Sangwoo too, I mean using his feeelings for him as a distraction to keep himself from dwelling on the fact that he did it.
Wtf have I just read