My ex left me after 5 years ago in the same manner. I came home from work (3 days before Christmas mind you) and she was gone and a Dear John on the door. There was no fighting beforehand and no sign that anything was wrong. She pretty much told me that same thing. The next step is difficult to decide and everyone has to choose their own way. It was different for me in that there was not a kid involved. I kept the divorce amicable and split our stuff 50/50, but I made her do all the leg work and pay the legal fees out of her own pocket because I didn't want the divorce.

Hang in there. A path will open up. Just keep your eyes out for it.