I still feel like this is all some horrible nightmare that I'm going to wake up from.
I'm so sorry for what he's putting you through. It's not a dream but you must wake up!
Others will disagree and tell me I'm wrong, but the rules do change when there are kids involved. You are going to have to interact with your H for the next several years. There's no way around that. You have to get to the point to where you accept that her isn't the person you thought you knew even though he is the father of your child. It makes it that much harder, I know. The fact remains, as unfair as it is, you have to let him go be where he wants to be and with whoever he want to be with.
It's no easy task and you shouldn't have to be going through something like this. But you are. Get back to him giving you what he owes you and what you deserve and only deal with him about your DS. He's not worth the time of day from you.