Oh, Emily...
I am so sorry that you had to experience this abuse from your H. I grew up in a rather physically abusive situation and I understand how demeaning it can feel to be hit as if you were a dog( not that I would hit mine...). You are a wonderful young woman and never deserve to be touched violently by anyone.
I think that if my H had just informed me that he just knocked up the OW I would have certainly done a bit more than yelling. He might well have found himself dodging my cast iron skillet collection. My point is that this sort of informtion would be very difficult to process and most people would likely not respond positively. He had no right to hit you. He is not a man. He will likely do to Cassie all the things that he has done to you and possibly more once his bitterness over what he has lost develops. God help her, she obviously doesn't understand the place where she has put herself. You however have already been helped and now see that you and your girls are more important than that loser and I am so glad for you.
If you can limit his access to your kids ( supervised visits) for a while that might be a very good thing as well.
Anyhow, I am proud of you. Let your family take care of you now so that you can all heal.

We're all rooting for you...

SW