Be glad that you found the discrepancies now...and can be aware of what you need to do. Being off budget every month by that much can start the domino effect of maxing out credit cards, HUGE late fees, over credit limit fees, cash advance fees for ATM purchases and the big shuffle off borrowing from Peter to pay Paul.
If there is any way you can cut off the spout, please do so before it gets worse. because of his overspending, it's you and the kids that will pay the price and go without.