Inviting my Moms bf to my wedding

My fiancé and I are tying the knot at a courthouse and having a reception a few months later. My parents have been divorced for four years and this will be the first time that they are seeing each other. My mom has a boyfriend that my dad does not know about and wants to bring him to the wedding. I don’t have a problem with him but he also isn’t my favorite person and I think tries too hard and want to replace my dad. But I know it will not sit well with my dad if he’s there. My dad is also paying for my wedding so I want to respect him. However, my mom is not taking it very well that her boyfriend isn’t allowed at the wedding. My mom’s boyfriend also never has anything nice to say about my dad even though he doesn’t even know him and only goes off of what my mom says. My mom was the one that walked out on him and moved. So I’m just lost as to what to do because I have a feeling if I don’t allow my mom to come, she won’t either and I feel that’s more of her problem than mine and if she chooses a guy over her kid that’s on her. Any advice if you’ve been through this