You make him go to therapy for his gambling addiciton, take charge of your finances and let him do more parenting with his children.

It sucks but its still not as expensive and draining as a divorce. Couples counseling on top of that so you can have a outlet, too. The debt is still considerable managable. He will have to work harder and longer hours, so while shit is being set up, let him spend time with his kid so you can take care of some of the steps needed.

Make it very clear that you are at a loss and that he will have to show, through actions, that you did not chose the wrong person.

Sorry this is happening to you. I would also suggest to get a financial consultant.