I went through a similar situation not too long ago where I made the decision to leave my best friend. Given, nothing really pressed for it to happen and it was completely all my decision, but I chose to keep my boyfriend over my best friend whom I had known a little longer and had become very close to. I don't regret it, to be completely honest. She was causing me to point my anger and frustration towards my boyfriend due to her own issues and pointing fingers because he wasn't perfect, at least in her eyes. Most of it had to do with myself. Now, instead of focusing on or thinking of how he's not perfect, I usually tend to think about my own flaws and them alone - it's not healthy at all, but I'm happier in a sense.
Depending on what you mean by you hear her name constantly, I'm going to assume he's constantly talking about her and it bothers you that he's so focused on her all of a sudden. In my honest opinion, any man who is fine with sharing his body with another woman other than the one he claims to love is lying. I'd go so far as to include my opinion on men who watch porn and try to justify it, but that's my own opinion. If you need space from him, on the other hand, you should tell him about it. Truly, if he does love you, he'll do what he can to make you happy. As for the mother thing, seeing as how my boyfriend's mother doesn't like me purely because I made it clear I wouldn't join everyone else in his family in treating her like a perfect little princess, all I can say is that it may or may not be because of her own issues and that you more than likely haven't done anything wrong, but you can ask your boyfriend to try and help to figure out what her problem with you is.
I know none of this is easy, trust me. If you need anyone to talk to, I'm here for you.
