I can't recommend what Gretchen should do about her husbands behavior. Three stints in Rehab sound to me like somebody who wants to give the appearance of wanting to change, and may consider the idea a possibility, but the sincerity is missing.
I have had to deal with my husbands extramarital affairs. When I finally realized a couple of important things (#1 I COULD survive without him and be happier and #2 he was not going to change unless I drew a real clear, real strong line in the sand) we then were able to start fixing things. Infidelity hurts - and in my case, just about made me lose myself - I felt crazy (this was not a one time thing and was not ever a one-night-stand for him; he was out looking for other people to validate him and approve of him, and as a result had some rather superficial, but none the less serious relationships.) About a dozen sessions of marriage counseling and then a year and a half of psychotherapy for him, followed by some therapy sessions with our children, have gotten us to a place we never were; there is mutual respect, mutual appreciation, and he's the person I thought I saw when we got married.
I hope anyone in a relationship that hurts can step back and evaluate it - realistically. Is this what you thought you're life would be? Do you deserve to have to deal with all of the crap in your life? If you do, then change yourself. If you don't, then make some demands of people in your life who are making you miserable.
