Dilemma of friendship!

A friend told me that she saw her old boyfriend (who she hadn't seen in like 10 years or something) and met her family. Since then, they have been sexting and she is thinking about meeting up with him alone to have sex. Obviously her husband knows nothing and his wife probably doesn’t either. My dilemma is I know this lady and her husband have had some pretty big issues over the past 5 years and she won't have sex with him due to this. She told me all of this knowing that I wouldn't tell others we know or say names, etc. What would you do with this knowledge? Talk to her and see where her mind really is? Drop the bomb on the husband? Try to find the ex and alert him that someone does know and see if that changes his demeanor? I just don't see this ending well for anyone involved.