I feel like he let the Uncle comment slip; was it a good thing to let slip? No.

I was thinking the same thing. He had a evil grin when it came out but Sangwoo was not amused.

I think he said that to purposefully make Sangwoo jealous.

Def, and he is starting to see their relationship as a "real" one when I think Sangwoo is just trying to make sure he has and will always have Bum under his thumb, especially after all the shit with the cops. Maybe that's why he's trying to make Bum feel like he cares and wants to do normal couple shit with him.