Sounds like your wife can be depressed or bi-polar. Expect insanity.
An affair is a roller-coaster at times. Remember? Up-down-up-down-up-down....some people get suicidal during affairs.
You see, the problem is her. She's trying to find a solution to her unahppiness by having an affair. It's a temporary solution.
Muddle is right, being "in love" releases endorphins, adrenaline and a whole host (legion) of chemicals that make the person euphoric, and, at times, unaturally calm. These get triggered by contact with the other person.
When she's with you she feels pain, grief and guilt. When she's with him, she feels good. It can happen in 5 minutes. It's like pavlov's dog -- she's been conditioned feel good around him.
It's not fair. Who said it was?
Ride it out. Sooner or later, his shit will start to smell. The chemical length of this state is anywhere from 6-18 months.
