I can't imagine any sane judge would find for the plantif in a case like this. After all, the cheating spouse is far more to blame than the other woman/man. I doubt very seriously she forced him to have the affair in any way. Your best bet is to try and hit him as hard as you can in the divorce if you live in a "fault" state...
The only people out there that really have any real legal recourse are the ones who's spouses or "other woman/man" happen to be in the military. Adultry is a UCMJ punishable offense, and they do tend to take it pretty seriously. I saw a few people get in quite a bit of trouble over it when I was in the military...