Hi sky3421.....that's a pretty big issue, I can tell you're very upset about it. But the fact is, IF you decide you want to stay with your bf, then your mom will just have to deal with it. If she wants to be childish, then so be it, BUT you don't have to be. If you bring your bf around her, just ignore it if she ignores you.
In other words, your bf is in your life, and there is no reason why you have to enable friends or family to treat you and him with anything other than respect. When your bf is in town, and you want to visit your mom, bring him with you. Treat the experiance as normal, and expected, whether she likes him or not. If you refuse to acknowledge childish behaviour, most of the time, it stops.
You'll have to be patient, of course, because it appears you are going to have to act like the adult in this situation. I've been where you are right now, on the other side...my ex-hubby's mother was a true monster-in-law to me because my ex didn't marry the woman she'd picked out for him. My ex just brought me around her, which was awkward at first but ended up making her behave. Took time...but was worth it.
Of course, then I divorced him, so she got to say 'I told you so' to him

but for the years we were married the witch had to act right!!!
Good luck and don't let your mom run you.