Sounds like he's trying to move on and you're still grieving. Unfortunately if he doesn't want to talk that puts a problem in the middle of all this. This may sounds backwards but have you talked to his gf about this stuff. Be careful how you word things though make it more about missing your mom than that feeling of her creeping into your fam. She may be able to talk him into hearing you out. If she really cares she will listen and have your back. If, however, she turns out to be awful then all that is required of you is to tolerate (technically not even that but it's better long run). If things get dicey come back or msg. I've dealt with different circumstances but same issue (dad won't listen and gf didn't get along with me).