You posted "I shouldn't throw this away just for money" WW and your post has left me wondering what exactly you'd be throwing away.
There's no mention of your relationship other than from a financial aspect. You don't mention shared interests and there's no mention of love so why are you with this man?
You will have no security if something happens to him in terms of where you'll be living, and without wishing to sound unfeeling, this is something you need to think about very carefully.
"I think he'll be devastated if I left as he'd lose such a lot in terms of personal/family value" but he doesn't appear to put much value on you, your children or your GC. He bought far more extravagant gifts for the D he hasn't seen for 5 years, her choice I know, and for a female friend neither of you really know than for you, and nothing for your children and the GC who seem to be far and away the main contact with family that he has.
You don't say how old you are but that financially your are "okish" and "can survive".
I agree with Oopsadaisy it's as much about control as money and in your situation, I would be seriously questioning the long term prospects for you in this relationship and if I'd be better off, in terms of financial, practical and emotional security without him.