Oh, this one of the most upsetting posts I've read.
It's like he's punishing you for having children that he willingly concieved. It's wrong and so unfair.
You seem far too good for him, kind, articulate and a lovely mother.
I understand why you haven't left. The thought of even less than the very limited support with your children is frightening.
I think you need to look at your situation with a professional (solicitor, social worker, women's aid etc.) from multiple fronts and see what's the best way forward.
I don't know how to write this without adding more burden to your difficulties but if he left you tomorrow, how would you manage the care? I suspect that he would either have to continue providing it or fund it by way of court ordered payment.
If you think about it this way, maybe divorce may seem more palatable as at least, you will be the deciding party.
Check out your entitlements both finically and with support and respite if you were a single parent.
Have you spoken to any family about this?
If you are due inheritance, it could be left in trust for your children or of there's a property involved you could be giving a right to live in the property.
Have you any siblings who could support you in any way?
I strongly suspect that you are doing all of this for your children, on your own and no one, not even family, are aware of what you are dealing with. Is there anyone that can support you, even emotionally?
I know you say divorce isn't an option but please at least talk to women's aid and explore it with s solicitor before you rule it out. It may not be an immediate option but try to see if you can start building towards a position more palatable than this.