For what it's worth, I agree with this post 1000 times over. It's hard to say, and even harder to hear, but you must break out, by yourself and for yourself. And much better to do it while you're still young. As other posters have also said, some counseling will help you, and I strongly advise that too.
The question of whether you earn an MFA or PhD, or five PhD's, is really irrelevant. You mother is running your life, and you must take charge of it and break free of her.
Feel free to personal-message me if you'd like any further details, my own broad outlines are very, very similar though the details are totally different, in fact, opposite.
Been there done that. You don't want to follow in my footsteps.
Wishing you all the best!
John