Nothing he tells you will be the truth right now anyway. He'll only lie, and the truth is HE probably doesn't even know "why" he's doing what he's doing. He's confused and selfish right now, and it's his battle to sort out and you can't control it or even really STEER it.
All you can do is work on yourself, and lay out (and enforce) healthy boundaries for you and your sons, which you've done a really good job of.
You can't "teach an adulterer," but you CAN occasionally get in little "truth darts" that MAY get thru to them somewhat. If he says he's "having fun" again, just say something like "Well, I'm sure your sons will understand your leaving their lives so long as you're having 'fun'." or "Is that the kind of character you want to teach to your sons?"
Other than that, there's not much you can do other than protect YOURSELF -- legally, financially, emotionally, spiritually.
