@Littletreeboots
I'm sure it's been mentioned already, but beg, borrow, or steal the money and see a solicitor immediately. Prepare notes wrt the family finances (income/expenses), savings/investments, pensions, and importantly, the house. Do you own/rent? If own how is the house titled and was any money 'ringfenced' either for you or away from you? It doesn't mean you are going to 'do anything', it just means you are educating yourself as to what divorce may mean to you and knowledge is power. That knowledge will also allow you to make other decisions that need to be made.
File for CMS if the solicitor advises you that the time is right to do so. File for whatever benefits you may be entitled to. I'm in the US so I don't know exactly what it is, but posters have advised women in your position that there's something you can do wrt council tax, change it to single?
I know you're exhausted, I know you're terrified. I know that seeing a solicitor, filing for benefits is acknowledging to yourself that he's not coming back. And that's scary. But I also know that you have sources of internal strength that you don't realize you have. We all do. So know that you aren't doing it for yourself, you're doing it for your children's future. Dig deep.
And forget about an OW, for now. The time will come when you can cry and rage to the skies about his cheating. But that time is not now. Now you must protect yourself, and by extension your children.
You say "I have family but there (sic) not supportive in the way I need them to be". Stop a moment and give serious consideration to the ways they would be helpful. Even if it's not the way you want them to be, is it 'enough' that it would make a positive difference if you were closer to them? If the only support would be a shoulder to cry on, that's most likely not worth moving for. But if they could provide even minimal 'practical' support, would it make enough of a difference to make it worthwhile? Obvs, if you own your home that comes into things, too.
You will get through this. Your life won't be the same, but it will be the life you make for yourself, and self-determination is always good. Thousands have been where you are, thousands will come after you. You are not alone.