looks like he married her on the rebound and got it badly wrong. And he seems to realise it, which is a big step to make - a useful learning experience for him, which is good news because it means he'll have got some foolishness out of his system. (Lots of husbands haven't.)
Regarding jealousy, though, most people's partners have some sort of history, and there's nothing much anyone can do but shrug their shoulders and say 'Well, he's with me now.' I suspect the longer he's with you, the more the doubts will fade. Just remind yourself you've done nothing wrong; any mistakes were his, and you've got what many would see as a fairytale ending.