I know that conflict is going to make things harder for you with the way you're feeling at the moment. I wonder if he is thinking you are trying to punish him by using the baby? He needs to understand that the hospital stuff is not about the baby, it's about your wellbeing in the incredible emotionally and physically challenging time about to come. I don't know how he would take it, but maybe you could clarify that you will be open to discussing visitation and things but you need to get through the birth first. Maybe point out to him that although he no longer cares about your wellbeing, your wellbeing is in fact extremely important because your son needs you to be healthy and functional.
Also, how did he know you've taken him off the paperwork? You're not obliged to tell him anything you do from now on - of course you can if you wish, but he doesn't get a right to know the ins and outs of the choices you are making unless you want. You can fob him off about the birth saying you're still deciding what to do, and then just don't tell him until afterwards. If you want to.
Reading between the lines, and I say this not to upset you, it would be good to get yourself in a mindset where you don't rely on him as a father in any way. He could be a beautiful dad, or he could be the dad that is around when he feels like it or changes plans for a better offer (my FOB is all three of these things!). Make your decisions about yourself and your son.
I know contact with him is upsetting you, and I think it would be good to cut contact with him as much as possible. As you work through the stages of grief that might be easier at some times than others. I just want to remind you of this:
He didn't confess, he was caught.
Even so, you forgave him and decided you'd try and make it work.
He couldn't keep to the agreement he made and continued to see her.
HE has been the scumbag here. He is angry at himself and lashing out at you. Even if what he has said to you about his feelings for you is true, he showed you no integrity, compassion or love whatsoever. He was too gutless to have difficult conversations. Now he wants to go through the motions in a fake life with you while doing exactly what he wants. I've been there. There is no loneliness like it.
I won't say he's a bad person because I know you love him, but at the very least he has handled things in an appallingly gutless and hurtful way.
Honestly, if the messages get too much I would just write 'please leave me alone. I need space and your anger and aggression is distressing to me and our son.' You don't have to respond.
Hope you're doing ok.