I'm sorry, this is very sad. But you have to face the fact that he said the word 'divorce'.
He is very disrespectful towards you and frankly, so very immature to say & do the hurtful things he is doing. Can I say, What A Jerk! You are not his doormat. You are the mother of his child and deserve respect. Oh, and you are still his wife. For now.

This younger lady is not getting any bargain. She wants a guy who cheated on his wife who was on bed-rest while carrying His Child? Wow! What a guy. Doesn't sound like the guy you thought he was. He is showing no honor or integrity. And he is just cruel to flaunt his infidelity in your face.

I would ask him to move out immediately. Have a friend over if you must for moral support and pack him up & get him out. You should not be available to be humiliated by him. And he should not see you crying over him, that only feeds his ego right now.

I would talk to an attorney asap. I know you want him back but getting information now will keep you focused on what may lie ahead. You need to do this. He's the one who said divorce, so ask around, and find the very best family law attorney you can.
Get started taking care of you & your child. Do something extra for yourself too, maybe join a zumba class to get out that extra emotion/sadness/anger in a healthy way. Plus the bonus of that is you'll feel and look great.

If you are holding out hope that he will snap out of it, you stand a better chance of that happening by being unavailable to him. He may realize what a dope he is. He may come to miss you but he can't miss you if you are always around. But don't pin your hopes on that. He is, as you say, infatuated with someone else now so it may take some time for that to wear off so he can see clearly. Again, I'm sorry.
Now, Please take care of you.