Mom Vs Fiancé

My mom and I have ALWAYS had an up and down relationship, we used to constantly argue, up until recently I’m just getting to the point I give up. So my fiancé and I have been together 4 years and we are expecting our first child together in a week! ❤️ he’s been around to witness some very toxic arguments between my mother and I. He’s always been super frustrated and there have been multiple times she’s disrespected him! And I beg him to not say anything. Recently I noticed him saying things back to her, especially when she says things to me that he doesn’t like or finds disrespectful. I’m in a REALLY crazy situation, I love my mother and I really love him. But things are slowly becoming explosive. What do I do???