He needs counseling. He also needs to be put on a rather short financial leash. You are going to have to be the grownup here. That means taking command of the finances, having his checks directly deposited if they aren't already, and he gets an allowance for his necessaries (e. g. lunch money, gas money, that sort of thing) and nothing else.
Are you treating him like a child then? You'd better believe you are, and I am advocating for that. He is a big boy, but that kind of gambling destroys families and you need to protect yourself and your children's futures. If he balks about this, you might need to go to the nuclear option. I'm serious. He could gamble you into homelessness, and that ****'s gotta stop yesterday.