Ok, yes, this is entirely predictable and par for the course.
OP, as much as you can, stick to the outcome you need.
Don't get into lengthy discussions about why, what, and wherefores.
He will blame you for everything (it doesn't matter).
He will tell everyone else that it's your fault (who cares? you will have what you need).
He is moving past bargaining (although if demands and threats don't work at first, he may cycle back to the bargaining stage).
This is all you need to remember:
You wanted your house back.
You wanted not to live with him and his children anymore.
You wanted to perhaps keep the relationship going after he moved out, but he doesn't want this, so you will have to let that go.
You want peace and quiet.
You want your life back, and to feel whole and happy again.
The most you can manage right now (Day3!) is relief, sadness, a bit of acceptance, enjoyment of your time again, especially with your son and friends.
And building up your strength and resilience, which you will never be able to do if he is around and poking you all the time with accusations.
I think some previous posters had some good suggestions about limiting the time you spend reading his panicky tantrums. He got himself into this situation, he can start being a grownup and get himself out of it.
THIS IS NOT YOUR PROBLEM TO SOLVE.
He will blame you for everything, let him.
He will accuse you of being the problem in the relationship, let him.
He will say you never loved him as much as he loved you, let him.
He will eventually start coming up with cruel things to say to you to make himself feel better, let him.
You do not have to read the messages.
If you do, you do not need to respond.
If you must respond, it should be only to clarify something administrative that needs to be done.
You have what you need. I know it's not the same as having what you wanted, but need is more important right now.
Stick to your guns. He is melting, and will soon start to spontaneously combust because nothing he is saying is making you change your mind or say yes. He wants you to apologize, forget everything that you said and made happen, and take him back, with no conditions.
Unless you are going to do that, NOTHING he says has any power over you.