@Broke and Alone,
First off, I'm sorry this is happening.
Now think objectively about your financial situation. Can you pick up more hours at work? Even if the kids have to be home schooled, you may be able to grab an hour here and there.
Do you have commingled funds with your GF or do you each have your own accounts? If funds are commingled, open your own accounts and start socking $ away. Your GF should be paying 100% for her kids' care, education, food, clothes, etc. If you have foot the bill for any of that, stop yesterday. And ask for that money back (particularly if you have receipts. If you haven't been keeping receipts, start now. And yes, that includes taking them for fast food).
If she complains, let her. She makes more $ than you do, and they are her kids, not yours. They are her responsibility, full stop. She is damned lucky you're around to care for and educate them.
Stop doing the housework. She can afford a housekeeper or someone to come a few hours per week. Yes, even in the age of Covid, someone can come for a few hours and do the vacuuming. If she complains, again, let her. The house is hers, and it is her responsibility alone. You having to do the chores makes it impossible for you to work full time, and you want to (er, you do want to, yes?).
You have essentially been working as an unpaid au pair, chauffeur, cook, launderer, maid, teacher, etc., and for how long? Your time isn't free.
Yet again, if she complains, then let her whine.
If you're afraid that by creating these conditions, she will kick you out, then yeah, that may very well happen. But that seems to already be kind of in the works, anyway.
Consider ways to not become homeless. With your family out of the picture (every single person in your family? There's no one who you could hold your nose and make peace with? If there is, then do so
now, before things get dire), look into roommate situations. Any local college will have cheaper housing nearby and people who need to share rent and other expenses. Be prepared for, potentially, a loud party here and there (yes, even during Covid). Take safety precautions and continue to save your $, even if it's just a few cents in a jar every week.
You are working toward financial independence, and that doesn't happen overnight.
BTW another potential source of funds is to borrow against any retirement $ you have, if any. While you'll probably take a tax bath later (talk to an accountant to be sure), worry about that then. Right now, you need rent $.
But do consult with an attorney (most initial consultations are free) and ask if your state has palimony or common law marriage laws, or if they have cases which follow (write this down)
Marvin v Marvin, 18 Cal. 3d 660 (1976). Wikipedia has a decent article on the Michelle Triola/Lee Marvin palimony case. See:
https://en.wikipedia.org/wiki/Palimony
5 years may be enough or close to common law marriage (see
https://en.wikipedia.org/wiki/Common-law_marriage#United_States ) in some states. 7 years is generally the minimum, but Texas and Colorado don't seem to have a time minimum, and for Utah it's apparently just one year. And note that the absence of common law marriage being an option does not mean that palimony is off the table.
Like I said,
check with a lawyer. Please don't just cherry pick advice off the internet from people who may or may not know what they're talking about.
While there is obviously a large emotional component to this, you will not be served well by concentrating on it. Rather, you will serve yourself considerably better if you just think of money right now - how to get it, how to get it back, how to get access to it, how to earn it (could also be through the sale of possessions, particularly if you have jewelry or the like), how to save it, and how to get interest on it.