I understand your hurt and anger at this woman. However, why would you want to get involved in their battle? I understand you want to help HIM (in which you are emotionally helping yourself by ‘getting back’ at her), but it seems more trouble than it’s worth. I’m not sure of the legalities of the out-of-state affair. If she’s not leaving her husband for you, then AofA doesn’t seem an issue-especially if she was already separated. As far as the CC goes, your admission of it would only make you look bad and guilty IF he is able to come after you in that suit.
I would just leave her to her own demise. Cut your losses and move on. If she’s trying to get alimony, then the affair would negate that, but you’d have to be ‘tight’ with either him or her to get that information. I would just leave well enough alone.