I think it would be best for you and your H to talk with your son together about the future. Let your H be the one to say it is his desire to leave the marriage but you should be there.
You can't take back what happened but in the future I would tell your H that any legal business will take place through your attny only. You have enough on your plate and honestly, your H isn't that responsible with money as it seems. If he can't support two child support payments he should have thought of that before he got OW pregnant.