How does this even happen? I'll never know either. Very few of us ever will.
SadSad, Alone... same here, except I was the provider; now she has left because she couldn't stand "living in my shadow", and I miss her so very much and just don't understand.
It's okay to not understand. Own what you can own, and be the best you that you can be, but know that so very much of this is not really your fault at all.
