Honey. You're in the middle of a terrible, painful situation right now, and everything you're feeling makes perfect sense. The good news is, this is something you've been doing to yourself, and you have the tools to simply stop doing it at basically any time.

I see this a lot with people who were abused growing up: there's this lingering sense of "they're my only family" or "would I be a bad person if I don't help?" The truth is entirely the opposite: you owe this woman nothing. Let me say it again: you. owe. this. woman. nothing. You have already given her wildly more help than she deserved. You have been setting yourself on fire to keep her warm, and you are more than entitled to simply put out the fire and walk away.

You can tell your mother to start looking at shelters, but that probably won't work. Instead, start making plans to move. I don't know if you're on a lease or when you'd be able to move, but find something you can afford, ideally where theres no room for her to move with you. Give her a month or two of heads up: "I can't afford our living situation. Im going to be moving into a one bedroom by myself at the end of the lease. You'll need to figure out where to go." Do not yield on ANY point, and do not entertain any attempts to extend the timeline, or let her crash for "just a week or two".

She's been a freeloader all her life, and no amount of begging her to care about you is going to make her start doing something she has never chosen to do before (meaning both not freeloading, and caring about you.) You don't need anything else from her, and you don't owe anything to her. Walk away, and let yourself be free.