I'm so sorry for what you are going through - it must seem like a bad dream that you wish you could wake from. I do hope you are getting lots of RL support.
Like others, I would lay bets on there being an OW on the scene - nothing else fits at all. I also suspect she is the link with the countries he's visiting now. If you can do a bit of digging, I'm pretty sure this will come out. I'm sure he will deny, deny, deny, but this silence and cowardly E mail communication all points to a man who doesn't want confrontation about how awful he has become.
I'm afraid that nothing absolutely nothing - turns a previously caring, loving DP into a cruel, unfeeling bully, like an OW. It's such a well-worn script, as many of us will tell you.
In your position, I would call his bluff now and tell him you know about her and who she is - and that you will be taking your own actions in consequence. Be enigmatic and perfunctory - get him on the back foot wondering how on earth you know so much. Don't reveal your hand until you get more information. Don't plead, beg or show any emotion other than anger and contempt.
And when you have done that brave thing, dissolve in tears as much as you like with your real allies.