Fiancé Dislikes Our Cat

My fiancé and I got a cat together. We’ve always wanted to get a cat together but now that we have one, he dislikes her. It’s mainly due to the different smells she has. She has a very stinky litter box and the smell has kinda taken over the bathroom. I’ve tried to ease the smell but idk what to do. Our cat isn’t mean to him, she’s a very sweet cat. My fiancé is just really sensitive to smells. I’ve asked him if he wants to give her up and he’s said no multiple times. Any advice is welcome because this makes me really sad.

(Her name is Lilly and I love her)