This man is not your friend, and you must stop trusting him or believing anything he says. If he says the sky is blue you make sure you look out the window to check, you don't take his word for anything.
He has lost his right to bore you with his opinion of your behaviour as he's decided to fuck off so you and your behaviour no longer have ANYTHING to do with him.
He has zero understanding or compassion for the utter annihilation he has cheerfully rained down into the lives of you and your children.
Don't let him back in EVER, you are far far too good for him.
He is also so stupid not to realise that he will lose the respect of his children; forget the Disney dad stuff he's indulging himself with for now, they will remember that YOU are the one who is there for them, make no mistake about that, and they will grow up knowing Dad behaved like an asshole. I can't think of a bigger loss than that and the man you describe won't even appreciate the true value of his children's good opinion.
So don't go thinking that he and his new setup are the bees knees because they aren't.
It doesn't feel like it right now, but actually the rubbish has taken itself out, and you and your little ones will be absolutely fine, believe me.
And please don't think about ending it, which I understand completely as I felt like that myself, but he is so so not worth it.
Either he is so pathetic that despite DESPERATELY wanting to make it work out with you, his penis just accidentally fell into a random 24 year old who happened to be passing by, or he's messing with your heads and enjoying the teenagery angsty drama of stringing you both along by telling you and her everything you want to hear. Neither version is attractive or desirable or good enough for you and your children.
If you were to kill yourself just imagine him dining out on that one, (I'm sorry) regaling the tragedy of his life whilst secretly his ego is dancing and thinking "Wow! Get ME !!! I am just SO AMAZING! I can prove it!! LittleRay loved me SO MUCH she actually had to kill herself because I left her!"
And finally, you are not wallowing in it, everyone takes their own time to get over this. It is not a crime or a failure to put your love and trust in your husband and you have been deeply wounded and you need to go through a grieving process to heal, so don't listen to that bollocks either, you have lots and lots of people on here all supporting you. Good luck x