If nothing else, it seems like you need a place of your own, a quiet place where you can bolt the doors, rest, and detox from all the toxicity that has invaded your life. If you can talk your mom into leaving that abusive ex, that's great, but don't wipe yourself out trying to do that. You have been surrounded by needy people who are clutching at you to stay and solve their problems for them. You need to take care of yourself for awhile, and let them find their own strengths from within.
Perhaps your triad won't completely sever, and perhaps you'll still have contact with your mom. But you need much, much less of these things for awhile. I almost think you need 1-4 weeks of sheer solitude, no interruptions at all, just a chance to lie down and think (or not think, better yet). Probably not possible as you need some kind of a job to support yourself, but at least make these toxic people stop invading your consciousness for awhile. You can decide what to do later, after you and they learn that they don't *have* to have you standing by seeing to (and worrying about) their needs all the time. Give your own needs a chance for nurturing. If you don't, you'll become a basketcase and won't be able to help anyone.
Any venting you can do here on Polyamory.com, please, do so, and let that be a way of spitting some of the poisons out of your system. People here will be waiting and willing to help support you and get you through this. Rely on that as much as you need to, and get lots more rest than you've been getting lately.
Love means never having to say, "Put down that meat cleaver!"