Mama's Boy

My boyfriend just recently moved out of his mama's house and moved in with me. Him and his mama are very close because it was only his mama and his sister living under the same roof for a while and he doesn't care too much for his sister. My problem is she calls at least once a day and he worries sick if he hasn't heard from her and will call her. Sometimes, it's 3 or 4 times a day and he waits on her hand and foot and she bosses him around like a child and they share day to day details sometimes he tells her stuff I don't even know yet. He claims he worries about her because she works 2 jobs and doesn't get enough sleep and one of her jobs is a factory and he is afraid something is going to happen to her which is understandable but when his phone rings, he jumps up like it's a fire alarm going off and it's frustrating because I feel everytime she calls I'm being pushed to the side. He acts like he has to talk to her that very second as if he can't call her back. We have been in the middle of serious conversations before and it got put on hold because of her calling. I have already talked to him about it and he said he would fix it but now he talks to her when I'm not around. He just called because he is out of town and not even 10 minutes into the conversation I can tell someone is beeping in and instead of telling me his mama is calling, he asks if he's interrupting anything I was doing in an attempt to get off of the phone. So now I feel like he's going to start lying to me. I don't want to make him have to chose so I'm going to try to deal with it but I don't know how because I can't relate and have never dated anyone that was THIS close with any of their parents or friends before. Any suggestions?