Dear Prudence,
My neighbor’s wife is having an affair. I know this because last weekend, I was next to the fence that separates our backyard weeding, and she was sitting at her patio table talking to her significant other on her phone about various sex acts they had engaged in the last time they were together. We were less than 10 feet apart (she didn’t realize I was there), and no, it wasn’t her husband she was on the phone with because at one point I heard her say, “There’s no way ‘Jeffrey’ knows about us.” Jeffrey and my husband are pretty good friends. Should I say something to him, or is his wife’s infidelity none of my business?