My feelings on this topic vary widely and depend on whether your boyfriend's a young man late in cutting the ties of adolescence, or a thirty-year-old stay-at-home who sleeps on a cot in Mama's room.
Whichever the case, know that navigating the web of your significant others' family is unavoidable. If your boyfriend, girlfriend, husband or wife are still talking to their parents, you're going to be doing so as well. And what's worse, your mate probably LOVES the hapless sons of bitches.
I'm not suggesting that love for your partner can't help you overcome friction you might have with someone on their side of the tree, but I think people often underestimate the impact marrying into a family has on your social connections.
If your man has serious, Psycho-level mommy issues, don't think that those will go away quickly, or that you pushing won't make him instantly and unshakable defensive, because it certainly will.
Things change, and so do people, but don't count on someone cutting ties with their family for you. Much better to find a way to understand his mom or relate to her in some fashion, even if that's just an uneasy truce. Then ambush the bitch when she least expects it.