Oh!! This makes me so happy that you enjoy him!! I’m still working out all his details but I like to think him and Serena have a decent relationship. Serena, after defeating her father with Sweeney, looked to him for comfort and he reassured her that this was the way things had to be. She is aware Sweeney has an ulterior motive for power. She noticed this after the death of Harkon, but due to her being a vampire and being locked away for so long there isn’t many other places for her to go nor does she find it worth it to stop him. Sweeney treats her well though! Especially since her blood is something he needs to have Auriel’s bow to work. He doesn’t wish to taint the partner like relationship whatsoever and does whatever he cans to fulfill her desires, wants, and needs.

She appreciates the things he does for her, even if it isn’t entirely out of kindness. But they do have their moments of genuine bonding.