Wow. That’s truly incredible. I can’t begin to fathom what is going on there. Have you considered speaking with a mental health professional? Maybe there is something else going on here for the change to be so abrupt?

I'm really sorry you're going through this. I have been blindsided before, I wasn't married to the guy but I was sure that he loved me so much and we had an amazing connection. It is really painful. But he pretty much cut off communication with me except for texts for a few weeks. Then I found out 10 months later he was getting married to someone else. So my first thought is that he is probably cheating on you and he was probably fake during your relationship.
The other thing is that some men prefer "logic" to feelings and so they make decisions base on what they think seems to make more sense to them, not how it's going to make you or anyone else feel. I know it doesn't seem logical to us but if they move on to another woman they have so-called "reasons" and the commitments they made to you and even the feelings they have for you don't matter as much.
I'm not sure what else to tell you to do, there is not much you can do to make him talk to you. He may be forced to talk to you at some point to work out details in your divorce but meeting through your lawyers can be very stoic. I suggest gathering morale support of your friends and family, and getting the best lawyer you can.