Glad to hear you are getting a little bit of a break at the end of this month, hope it helps you to make some decisions about things.
I am thinking you are living with BF and GF right now? You don't have to live with them to have a relationship with them. You can still have a place of your own. They don't need you around *all* the time.
As for your mom, she is a grown-up, certainly knows what she's getting herself into, and has the power to get herself right back out of that situation at any time. She is your mother; you shouldn't have to be her mother all the time. Express your concerns, especially for her physical safety, then respect her decision to plunge down that dark hole if that's what she's determined to do. It sucks, but it is her actions and her responsibility.
It saddens me that BF and GF are so poignant about begging you to stay, yet they refuse to change their behaviors that are driving you away. It looks like you are babysitting three adults right now, as well as trying to take care of yourself. Do what you can, know your limits, and get some "you time" to get away from it all.
I hope I can continue to offer thoughts and persepctives that are helpful for you.
Love means never having to say, "Put down that meat cleaver!"