AA, I am very sorry about the news, but your friend could have handled it much better than via email and w/a curt message no less.
Many mlcers are h@ll bent on moving ahead at rocket speed into a new relationship. Some even marry very quickly and since you and your SO were not married, he felt that there was no need to worry about a divorce and once he left, he considered himself a very single man. I would say that the new spouse has been in the wings for a little while, most likely in the last 18 months he met this person. I'm very sorry this news was dropped on you today.
Relationships that are built on lies generally do not last because there is the trust issue. However, some will live in misery for a very long time to prove that they did the right thing. I hope your SO will wake up some day and realize what he's done...but that's a long way down the road.
When you feel better, you will need to begin your life as if he will not return. No one knows what the future holds and for now, you have to take care of yourself. For now on, any discussions w/him are to be treated as "business discussions" and nothing more. Try to remember to view him as the neighbor next door and keep your personal feelings at bay. You've got a lot of things to do in the days ahead and you will need to leave the emotions out of any business dealings in order to think clearly about your financials, the house, etc.
AA, I am very very sorry that this has happened. I know how it feels to have this particular news dropped into your lap. Take some time to grieve for what you have lost. It's okay to to unplug the phone and lock the door for a while.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.