Why did his mommy get his way?

OK, so leave him and find someone else who's not such a momma's boy. If you don't get along with the family, it will never work. You can never expect to step between a man and his blood family, that never goes over well.. you will always lose out in the end. Especially when mommy has as much of a grip on him as this one's does. I'd never have gotten too involved with any man who was still as attached and needy towards his mommy as your guy. He IS immature, and that's not going to change any time soon.