BD, I am glad I turned my computer on at this moment and I hope you are there at the other end?
First of all, the biggest hug you have ever had is coming your way from me. I'm with you. This is how I feel about my WH and it's what happens when you let them back in your life when you are not ready. You weren't to know you were not ready, but now you do. It make take some time, weeks, before you shift again and it's important this time now is about YOU and processing what you are feeling right now.
I also want to validate you and say that no one could argue with how you are feeling. WH IS an alien and you don't need the alien at such close quarters right now. It's your call - and you called it. That's fine. Right now, YOU make the decisons. Not him. OK? And you be proud of that.
You have been treated like utter sh!t, but you are not disgusting for trying to be the bigger person and make the best of a very, very, very hard situation. You are courageous and all of us admire your strength because we know what it takes. This is you reclaiming your dignity and asking a very important question: is your H an alien currently wizzing in outerspace for whatever reason, or is he a man of value you want to spend your life with?
I am not sure the answer is 100% there yet, but it's clear that for now you need some time out from him.
You do not have to fight to save your marriage. Not now. Maybe not ever. You can backburner this WH and his problems. You and the baby will be fine - everything you say is true and no one expects you to be perfect (what IS that anyway?). Your son will understand one day that you did everything you could possibly do. You are the winner, your WH is a loser (sorry, it's true).

Not that it really matters BD, but how did he respond when you said all that?

Also, if you change your mind later down the track and want to include him back in your life in some way (and you'll probably have to given he's the biological dad and super keen to be present), I don't think you have blown anything.

But that's not where you are at right now, so don't give that last para much thought!