I didn’t even know he was married, let alone to her. By Kwame Anthony Appiah Kwame Anthony Appiah has been The New York Times Magazine’s Ethicist columnist since 2015 and teaches philosophy at N.Y.U.

DEAR ABBY: My wife and I have been married 30 years. Over the last couple of years, a male friend of ours (also married) has taken an interest in my wife. He obviously finds her attractive, as most ...