I’m sorry you’re struggling but to break it down and make it as clear as possible, you can afford it if you want to.
You said you earn less than £2000 a month. With that salary, 2 children, private rent and being the only adult in your new home you are entitled to UC. A quick estimate calculation of around £250 a week, so there’s £1000 a month. Not including childcare which UC can also pay up to 85% of.
You’d also be entitled to child maintenance unless 50/50, so there’s some extra, if you know his salary you can pop into the CMS calculator to see how much you’d be expecting to receive there.
The house won’t sell overnight no, but it will sell, or he can buy you out. That money is then your pot to either buy or rent somewhere. If you were moving out with 2 children you could also apply to your local council.
You haven’t said why you want to leave and you absolutely don’t have to share that information here but if you are being abused then you can reach out to Womens Aid who can support you in the process of leaving.
Nothing is insurmountable OP.