He has been to jail over it once though. That costs him fines and time at work which comes back to bite my son and my ex-wife's other children.
That makes her even more reliant on income generated by our son.
My son doesn't want that on his head. He's told me that.

They usually get along okay, but the guy snaps every once in a while. Other than the adultery from 13 years ago and the periodic abuse,
he's a decent guy.
To the guy's defense, he does seem to feel terrible about it every time. No one will believe me, but he truly is normally good with my boys. The bad times are terrible though.

Last week was the first time my son has ever fought back and he snapped pretty quick. His step dad barely even touched him. It was nothing more than a little grab on the shoulder and it probably wasn't even very threatening YET. His step dad is about 6'3 and probably around 250 pounds, but my son has seemingly super human strength and he's freakishly athletic. He told me that the guy looked shocked as he slammed him against the wall repeatedly. He hopes that it will deter the guy from ever touching him in anger again.

My guess is that the guy is a little stressed out because of the situation in his home. With my son added to the heap, he's got 5 children in his house full time and he's suddenly having a rough time handling his mortgage payment because his greedy wife's ex-husband (me) is taking back almost $400/month of the child support payments he receives.

AND, my guess is that many here on cougarboard would take his side if they were his buddy.
the ex-husband is always a stingy guy.