I am so sorry you are going through this. Are you absolutely sure the idea of you not being invited is coming from his mother and not from him? Maybe his Mom is feeling in the middle. Maybe your boyfriend is using his mother as an excuse.
But any rate... it’s not fair that he’s leaving you at arms length. It’s not healthy for you. You deserve someone who loves you unconditionally and includes you in important events, like the holidays. I know it’s hard to move on, but if it keeps getting worse instead of better and he is distancing himself farther and farther away, that’s not a normal or healthy relationship.
Hugs to you!!