SOA, I just want to say your experience is similar to mine in that when the separation occurred, my H moved on pretty fast.
Therefore, I am going to agree with the PMA who said he probably already had one foot out the door to move on so quickly....
Either he was a time-bomb waiting to explode from past issues or he has been planning this for awhile and saw his opportunity. I'm just saying from my years of experience dealing with these type of stories. It is a rare occurence for a spouse to just walk without having another gameplan lined up.
Have you guys been unhappy for awhile? Why was he so quick to walk?? From my perspective it looks like he has been checking out for awhile. Or he might have been cheating on you as well.