Maybe it hasn't set in or maybe all that time you spent working just means you didn't have the same amount of love or commitment to him? Or maybe you were avoiding him because you knew your heart wasn't in it?

I also think that it's shock. Amateur author Dorian Wright describes similar feelings in their book "20 Years Gone: A Divorce Story" (avail at Google Books and Amazon).

Sadly, after that much time passes with someone, you don't really expect that bond to change. So, when it actually does, it kind of blows your legs out. Wright even compares it to being like PTSD (when actually, it really is).