What to do about this girl, the wife of my friend...............?

I would tell your friend that a woman like that is not deserving of him and that he should not waste his time with her. He should not feel at fault because he was not the one who walked out and went into hiding. He should just get a divorce. I feel for your friend and my heart goes out to him. No one should ever be played like that. Not all women are like that. He will find someone it will just take time.