He's not just acting
I know there are people who’s thinking that Sangwoo is faking his concern about Bum, that he acted like that because of the situation (the police station, everyone is looking and listening at them).
But I think (and I’m sure I’m not the only one) he was not acting at all. Of course, maybe he could’ve overacted, but Bum is everything for Sangwoo right now. The power that Yoonbum has on Sangwoo is enormous!
He was in pain in the previous chapter (here the scan)
And when the other officer put him in the car, he thought about Bum! (scan)
Also, the anger in his face! He could be the best actor but that was real anger, someone was touching and hurting HIS Bum and everyone knows how protective he is! (scan)
And when Bum hurt himself, what’s reason Sangwoo could have been to show such a concern about him? Obviously he didn’t act that time and the thing wasn’t that different: Sangwoo wouldn’t have been with Bum again, and here is the same concept. (scan)
I also think he was truly relieved when he saw Bum, it’s not a “now I have a possibility to make it” face, but a “he’s here” face! Bum is like an addiction to Sangwoo.
After that moment he could start thinking about what to do in order to escape from that situation. So yes, he could be use the situation in his favor and no, he didn’t act that much.
I’m trying my besto, im sorry for the english as always