This man is now a hero of mine. He tried doing things the easy way and nobody wanted to comply so he picked up a second job as a private investigator and blew the whole thing up. Good.
The cheater was probably sneaking around his wife for months thinking he was getting away with it and it turns out she was never the person he needed to worry about. It was the downstairs neighbor being kept up by thunderous sex with some time on his hands. Always be wary of who you're pissing off.
Now this guy just has to pray he did enough to stop the affair but not enough to cause a divorce, because then you run the risk of the affair just becoming the new relationship. That would be the ultimate Uno reverse card. Maybe send the wife a second email telling her to take it easy on her husband. He'll change.