Have you ever thought about how your relationship with your mother influences your choice of a romantic partner? It sounds like your GF and mother have some things in common. It's interesting that you can't talk to either of them about this, right? I speak as someone who recreated a bad family dynamic for years with various boyfriends

As for their issues with each other, I'd make the topic verboten. Mom, I am not getting involved. GF, leave my mother out of it.