If its a joint mortgage you can tell him to leave the family home and he can't sell it until the children are 18... Any probs making him leave get legal advice. This might mean that you become responsible for 100% of the mortgage though if he decides not to contribute, and in paying all that time you will essentially be building him a nest egg, so it's really only suitable as a short term plan until you can either buy him out or afford to make moves on your own (rented or bought).
But once you sort your single parent income things won't look so scary! Getting him out the house buys you time to do this.
Take legal advice if you're married re divorce and get evidence of his indiscretion because you might need it later.
Ring universal credit and claim as a single parent. Use the child maintenance calculator to see what he should be paying you for your child. Take what's yours out of joint bank accounts ASAP. Direct all your income/wages/child benefit to your single named bank account. Think about renting if you're low income because you will get housing benefit.
Change the locks.
Make these moves fast because once he realises you mean business and there is no going back he will be all about self preservation.
The house might seem quiet and you might hurt now but I promise it won't be for long. You'll find happiness again and you will look back on this and be so grateful he showed you his true colours
![Heart suit :hearts: ♥](https://cdn.jsdelivr.net/gh/joypixels/emoji-assets@5.0/png/64/2665.png)