I have not read all of the responses so forgive me if I repeat what another poster has said.

You need to stop giving your mom so much information. None of it is ANY of her business.

She's very controlling and will not give up that control easily. She will have temper tantrums and throw guilt trips your way (don't worry, she will not love you any less). I think you have to understand and process that information before you attempt independence.

You will have a long term relationship with a woman at some point. You don't want your girlfriend to think that you are closer with your mom than you are with her. She will leave. And I would not blame her.
The trick is to listen to your mom's "pearls" of wisdom, nod your head, and let it go in one ear and out the other. If she grills you about your girlfriend, then you need to either change the subject, or put your foot down and tell her outright that it's none of her business.

I cannot stress this enough: Agree with your girlfriend/wife. NEVER give any indication that you favor your mom's opinion. Ever.