Thanks for the response; she has cut off all communication with the OP. She has clarified that, while she was tempted, it never became physical and she has no real interest in the OP (he's married (badly), a borderline alcoholic and a known womanizer). His interest was the catalyst for her to move away from me but not necessarily towards him. My wife has always been a very moral person and I believe her on this issue.
The problem is, if she really did cut it off, she will tell you she cut it off.
And if she didn't, she will still tell you she cut it off. People who are cheating LIE -- period.
You're getting great advice here, so I have nothing to add, other than to please be careful and CONFIRM (independently) that there's no contact going on. Because none of the above is going to work if she's emotionally shut off to you, and she WILL be emotionally shut off if she's still in contact.
If nothing else, try the above for a period of time (4-8 weeks?) and if you don't see any movement, I would strongly suspect further contact at that point.