Your problem is not with the mom but with your boyfriend. If he will not stand up for you now, I doubt if he would do it later. I guess I have to take that back, the mom is a problem but only because he lets her be.
I really hate that he abandoned you at such an important time for you. Please don't give up on the fight for your bar exam. Personally I think you need that law license much more than you need him.
I'll never forget the guy that decided to tell my daughter the night before her cpa exam that he had a child he hadn't mentioned before.
If he doesn't love you and treasure you enough to be your support, there is someone else out there that will and you won't find him sitting at home crying about this guy.
Having said all that I realize that I have only heard your side of the situation and you shouldn't take a perfect stranger's advice about something so important to you.
May I share my favorite scripture with you? If not delete quick:
For I know the plans I have for you, saith the Lord, plans for good and not for evil, to give you a future and a hope. Jeremiah 29:11