(Thoughts as of Chapter 25, may change in the future as the story progresses.)
I think if Sangwoo ever kills Bum’s uncle or makes Bum kill him etc. it won’t be as simple as “let’s kill your abuser” but more something like “let’s kill him so all of your memories will be of me, you will have no one to return to.”
The relationship between Bum and Sangwoo isn’t that simple. Sangwoo isn’t going to suddenly jump in and start showing affection to Bum in a “normal” way. If he even starts planning the murder of Bum’s uncle we won’t even hear about it until it’s happening.
It is not jealousy, Sangwoo doesn’t care if someone hurt Bum before him, this isn’t about Bum at all, it’s all about Sangwoo. Everything he is doing is completely and utterly selfish.
Sangwoo doesn’t care about Bum’s past. The one time he talked about it, he called it boring. The only reason he got him to talk about it again is to establish more dominance because keeping secrets from him, as he says is “treating him like an idiot” which we saw him say he despises time and time again.
Sangwoo cares about his own past only, and he wants insert Bum into his own life, not put himself into Bum’s.