My first reaction is amazement that your H is trying to at least make it civil for you. My H would never send that email to me, ever, in a million years. Heck, your H owned up to what he did, doesn't want to make it miserable for you, and wants to basically be your friend for the kids sake. That is fantastic.
Did he lie, cheat, humiliate, degrade, yell, and everything in between? Does he still 'want' the D? Yes to all of that, but this is the stuff that isn't permanent. There is eventually forgiveness and possibly him turning around...
My advice (and PLEASE, I am no professional) is to send a short email back with something like:
"I understand now why you think I was 'shoving' you out of the house and slamming the door. That was not my intention. We are in different roles now and I am still getting used to them. I was nervous today.
Of course, I still care about you and want this to go as smoothly as possible for the kids sake. But you have to know I am struggling as I don't want this for us. I won't stop it, but don't want it."
This is just my gut. Wait to use my advice, I am sure you'll get better advice!!!
