Racer-X:
Here is White Horse's 4 step progam, chock-full of tough love.
1. I will second what Ross said. I have personal experience with this same sort of thing. Play the "husband" card and make sure your wife gets professional help, no excuses, no delay. It is the fastest road to recovery and well worth the hurt feelings your wife may have. She will thank you some day.
2. You broke her trust and created a hornets nest. Yuk. Block the nasty emails by filtering them. Use your answering machine for a while instead of picking up the phone. Realize that you can live without the relatives just fine. If this is how your wife's family reacts, she cannot count on them for support, compassion, or understanding. If this creep keeps up his hobby, they will understand some day, and it won't be so funny when it is their daughter/grandaughter.
3. Stay off the booze, or drink alone. Loose lips sink ships, marriages, friendships, etc. You were trying to help your wife (good), but a drunken confession is a bad first step.
4. You cannot tell your wife enough that it is not her fault, she is not a bad a person, and that you love her very much. Tell her 3 times a day until she is fully recovered. Be strong for her and the two of you will make it.
-White Horse
{Edited to add: Doh! Liberty beat me to it}