You can't solve this by yourself. There is no solution unless he wants to solve it with you, which involves him taking responsibility for his debts, getting his spending under control and being open and honest about things instead of concealing them. It doesn't sound as if he is prepared to do any of that.
For example, when you gave him money to pay off his "maxed out" credit card, he should have cancelled the card so he couldn't run it up again, not just gone out and spent up to the limit again.
He tells you that he's dipped into the savings account for essentials and joint stuff which should have come out of the current account - if that were true, why didn't he just take it out of the current account?
Seriously, with all his subterfuge, this is not going to end well unless he is prepared to make significant changes in his habits right now. I see someone else said you taking charge of all finances is you acting as his mother, but as you don't want to leave him, I don't really see an alternative. As he is seemingly incapable of controlling himself, he needs to give you the control over all the money and you can give him spending money just like a child. Yes, he will resent it. So will you. But what's the alternative? If he's not willing to do this then really he's not willing to make the marriage work, is he?
As to the mortgage issue, I fear what will happen if you take out the mortgage without changing his habits. Sooner or later you will go to make a mortgage repayment and find your joint account is empty. So as not to default, you will pay it out of your own savings. He will apologise and say he had a car repair bill to pay. Maybe next month there will be enough in the account to pay the mortgage, but a few months later, there won't be. So you'll pay it from your personal account again... fast forward a few years, your personal account is empty, your mortgage is in arrears... oh but at least your son is in a good school; shame he's about to be homeless.
You may not like the advice you're getting on this thread, but you know it's right; that's why you're here.