You are catastrophising.
Take a breath and, in a nice way, get a grip.
In your worst case scenario, you and your children live happily ever after in a rental that isn’t as close to your parents as you would like.
That is the worst case scenario. Now focus on the other scenarios.
Best case - he comes to his senses.
More realistic case - you get what money you can from him to support your joint children. File a claim for CMS. If and when he starts reducing his income, report him to CMS for having a lifestyle that doesn’t match his income. Do the same with HMRC. Do not tell him that you are doing this! In fact, don’t tell him anything. You have split up. Communication should be essential war dispatches only (so, child related only).
Get a solicitor. Get proper legal advice. Stop fighting what he wants just because he wants it. Instead, with legal advice, start fighting for what is reasonable for you and your children.
It is absolutely normal to have a bit of a panic when first confronted with a situation like this. But the best way to secure your future is to think clearly and move on.
(PS - if this sounds harsh, I want you to know that your ex is still a wanker and you are well shot of him)