How should I best handle this situation...Cheating husband?

Just make it VERY clear to him that if he messes up, he's gone. And if you make that promise, be sure to follow through with it. There is NO reason not to! You make your own decisions about what would mean a divorce, but make them very clear to him. Remind him that child support is expensive (especially for more than one child) and that it's good for 18 years. And that if he were to not pay it, the first thing the government does is suspend his license.