I'm very sorry to hear your story but is is similar to a lot I've seen and heard. In my honest opinion, I believe your wife has set her sights on greener pastures. This was not an overnight decision on her part. It doesn't sound that she had fully coped with her loss when the two of you married. Is it possible you were the rebound guy? You did say you were friends for years before it evolved into a relationship.
I don't mean to offend you in any way, just giving you different ways of looking at the situation. Best wishes to you...