I agree with garybuss. I have seen my sister jump from relationship to relationship, constantly looking for some kind of 'prince'. She is now 40, and just starting to realize that people are individuals first, couples second. Together is a choice. Life is so short, so full of crap, that to me, it is petty to stand ground and not take someone back if they are truly sorry and you truly love them still.
Now, about this post, we don't know the full story about why she left. After 28 years of marriage, looking back, was there not any signs at all of her discontent? My friend is leaving her boyfriend of 7 years and now that she has made the decision, put a deposit on another place, he is trying. He is begging and telling her that he will try now. But she is done loving him. She tried for years to love an unemotional, unresponsive man and she refuses to open her heart up again. There were signs for years, she TOLD him blatenly for years what was wrong, how she felt, what was missing, what she needed, begging him to tell her what he needed/wanted out of their relationship. Nothing. Now, he is surprised. Duh.
It was the same with me. 14 years of marriage. It took me 10 years to leave the abusive bastard. Once he knew I was serious, well then and only then was he apologetic, wanted counselling, begged, cried, wanted to talk, but the door, for me, was closed. I knew I would never open it to him again. To hear him now, he was shocked and surprised that I left him. Didnt see it coming. Intentional blindness to relationship problems is a choice.
So, my advice, there is nothing you can do other than learn from this experience. She didn't 'just leave' after that long in a relationship. Obviously the two of you grew apart and stopped communicating. I am so sorry for your pain at the realization of this, but maturity and moving on will require that you honestly examine your relationship with her. If not, like my sister and so many others I know, the balance of the relationship just carries forward.
Jez