And of course, he didn't even choose to marry you!!
Think about that OP.
I simply do not understand why women do this to themselves. You obviously knew he was crap with money, even before you chose to have his kids, but still went ahead and did it anyway, and now you're lumbered with a man who will take, take, take, and gives you nothing in return, but the fear of being in constant debt.
So now, if you decide to leave him, (which you absolutely should) you'll have no money behind you, and have the added burden of 2 extra kids. I know you will say that your kids aren't a burden, but in the reality of a situation like this, they actually are, as because your mother's instincts wouldn't allow you to walk away from them, you are the one who will now be stuck in the position of taking care of them in every way, until they reach adulthood, whereas they should be a SHARED responsibility, but the chances are, that if he won't even pay you back money he's spent having promised that he would, the likelihood of getting maintenance from him, is pretty slim.
I'm sorry if this feels like I don't understand your position OP, but it really makes me so fed up when I hear this story time after time.
So, in your shoes, I would make it absolutely clear that you won't be doing ANYTHING for him, until he's paid you back in full, and mean it. Don't do any cooking for him, wash his clothes, clear up after him, or have sex with him, until you've got your money back. Don't do ANY of the little things that we all do for our men without even thinking about them. Then, IF and it sounds like a BIG 'IF', you get the money out of him, pay off the credit card, pack your bags and leave! If however, you get to a point where you're absolutely sure he's not going to cough up, then obviously you still need to leave, but I think it's perhaps worth at least trying to get the money before you do.
Oh, and if you have any daughter's, please drum it into them, that if they want to have kids, they need to get themselves a good career, BEFORE getting pregnant, so that they are in a position to not only pay for a roof over their own head, but also that of any children they might want, as quite honestly, it becomes clearer to me every day that the vast majority of men, are selfish to the core, and cannot be relied upon to take care of anyone but themselves.