Do husbands regret leaving their wives/children for an old flame and does it ever work out?

My husband left myself and our 1 year old for his ex from 6 years ago. We've been together for 5 years this summer. I found out he was sneaking behind my back our whole relationship to see and talk to her, just as friends he says. But now they are in a relationship since we separated in March. He has nothing to do with me or our son really. Will they even last? Will he get what's coming to him... His family says that he isn't the same anymore too. I do not want him back but I just hope they don't work out since they didn't before, and that he realizes the huge mistake he has made. Does this usually happen when they leave for an ex? Or only when it's for a new person?