I'm not 100% sure this is on-topic. The essential core of the question is about a personal relationship and a personal issue. While there may be workplace aspects to this situation, none of them have been addressed in the question. Just because two people happen to work together doesn't make it a workplace issue.
The "Sleeping with my Wife" question is probably the most salacious question that I've ever seen on Workplace.SE. And in light of the fact that "sex sells" in Hollywood, who wouldn't want to discuss this issue on Workplace.SE?
But consider the verb I chose: Discuss
Is Workplace.SE really the best venue for advising a man about how he should confront a coworker who has been sleeping with his wife?