Hoping he will turn out to be a decent human being?
Oh come on love.
Even before you let him fuck you, you already knew he'd had a long affair and several 'party fumbles' (btw nice way to minimise CHEATING).
So look - you didn't "get him so wrong".
You knew from day one that he was a lying cheating cunt.
Stop putting wasted mental effort into working out how you got him wrong. You didn't. You know and I know that you really did know, underneath, that he was shit who just wanted the sex.
Stop wasting mental effort on shit like "he wouldn't have fucked me if he loved her". He doesn't love either of you - though he loves getting to be a family man and getting you to fall pathetically over his cock, that's true enough.
NEWSFLASH... I fucking despised my husband for several years because he was a cheat. Did I also cheat? No, I didn't. Honestly, I came close - the text messages I swapped with an ex towards the end of my marriage were not acceptable within a marriage. One reason why I finally left was because I knew I couldn't stay faithful any more. He didn't deserve my fidelity but he had it because I was MARRIED. I didn't leave before as I had a child with him - guess what love? Your shag's wife would have slung him out if she had no kids, I bet. Instead she humiliated herself shagging him MORE to keep her family together.
In fact, for this or the next married man with kids you fuck because of your "self esteem"
can you think about my daughter crying on Xmas Eve when she had to leave the fun at daddy's to come to me? And when she says sadly, "mummy, it feels like I see you more than daddy" or "mummy, I wish we all lived together". She painted a plate at Xmas and put our 3 initials in it, in a heart. 
That's what these cheatingCUNTS do to their children.
Why would you want one of those men? Why are they not an instant turn off to you?
So... Put your mental effort into working out why you chose to ignore blatant evidence that he was an arsehole, and fuck him anyway.
You were bored, lonely, selfish, whatever... but focus on you and your behaviour, not his. Because you're the one you can ensure behaves better next time.