Thanks to those who have given me their advice. However, since there are various suggestions/advice, which is little confusing to me, I would like to clarify the issue with some more details:
1) There is still considerable love between the current husband and wife.
2) The contact between the wife and the "Ex" over the phone and their plan to see each other is creating the complication in the current husband's mind.
3) The husband has recording of the conversation that shows they had in fact married when they were seeing each other 20+ years ago, without their parents’ knowledge. However, it seems from their conversation that their marriage either lasted for a very short time or did not last at all.
4) The wife does not know anything about the audio recording which talks about their marriage etc. The current husband thinks, revealing this would be ultimate and may break the marriage. He is still not mentally strong enough or prepared to call it "quits".
5) The wife was confronted by the husband about their contact with each other that, she was told, he found through their e-mails only.
6) They have two daughters; one is going to college and the other to high school.
Now the question is should he tell his wife about the audio recording to make her feel guilty and then get on with their life as is or take the risk of breaking the marriage?
I know it is more of a psychological question than the lawyer's question, but I would like to get some advice to the best of your ability, legal or otherwise. Thanks a LOT.