How to deal

My fiance is a mama's boy. Even his sister says their relationship is strange. And at first she didn't mind me because she felt like maybe we weren't serious even though we were together for 5 years at the time ( I would get little jabs here and there though) then after 7 years we had a son and engaged and moved into a new place and then it started 5o sink in. He'd always do everything for her so she'd save money, and she can easily manipulate him. So she'd come over excessively and strat throwing more jabs at me but in a sneaky way. And times where she'd be rude to me and he wouldn't be there or even if he was there she'd be so passive aggressive. And so I caught on and told her that some of the stuff I didn't like hurt my feelings and she took it as I'm sorry you thought I was being rude and tried to manipulate me and didn't like it. And she told her son that she never remembered any thing that she did but when she spoke to me again she said she wasn't trying to be rude. Even his dad (her ex husband) said that he doesn't like what she's doing and she's so subtle about it. I know my fiance should defend me but he's so blind. I've just let it go but I can't even say things like oh she dyed her hair black or I remember she told me she used to like this place without him snapping at me. Today he made fun of her new boyfriend and all I said was he was nice but his comment twiards me threw me off. And he snapped at me. I just don't know how to deal with it because I speak my mind I've never disrespected his mom. All I've said is some stuff she's done and said to me was hurtful. But its like he's blind. How would you guys deal with it ?