I guess the moving was inevitable but still another blow. Yes, I will be better for the kids, but even knowing that doesn't make it sting any less. Don't feel badly about your son questioning visitation. I'm sure he's torn and I would bet that it's hard knowing that his Dad is living 24/7 with someone else's kids. He's young but believe me he WILL figure this all out for himself. As he gets older he will probably resent his Dad for the choices he's made.
You're doing great and you'll make your own memories with the kids. Heck, you've already started. As far as ex and the way he treats you, well that's his junk not yours. He's got lots of problems and you happen to have been the one he was able to blame them on, but you know in your heart that it wasn't you.
Tears are good. They make you feel and deal with what is. With every tear there is growth.