The lie was so boring I almost respected it.

Most men cheat with hotel rooms and burner phones. Daniel cheated, I would later learn, in a fluorescent-lit warehouse the size of an airfield, pushing an empty cart past pallets of paper towels. He called them his "friendship walks." He said it with a straight face, the way you might mention you'd taken up jogging.

It started in the spring. He'd come home from the office, change his shoes, and announce he was heading out for a walk with Priya, a new hire on his team. Twenty-six, sharp, the kind of person everyone in an open-plan office gravitates toward. They walked, he explained, at the Costco off the interstate. Apparently the long aisles were good for clearing your head. Apparently you could do a loop in eleven minutes if you didn't stop for samples.

I didn't blink at first. What was there to suspect? A grown man wandering a grocery warehouse is not the opening scene of an affair. It's the opening scene of a midlife crisis with a membership card.

But the walks grew longer. Forty minutes became ninety. He started coming home flushed and quiet, his phone face-down on the counter, charging in a room he wasn't in. And one evening, when I said brightly that I'd love to come along, that I needed loo roll anyway, he turned to me with a strange gentleness and said, "No. These are kind of our thing. Mine and Priya's."

Our thing. As if a wholesale club were a sacred grove.

That was the sentence that cracked it. Because a friendship that has to exclude your wife is not a friendship at all. It's a relationship wearing a friendship's coat. I lay awake that night turning the word over until it lost all meaning, the way "walk" had already started to.

I didn't scream. I didn't go through his phone in a rage. I just paid attention, which is the most dangerous thing a quiet woman can do. I noticed the second toothbrush-shaped gaps in his story. I noticed he'd started buying things we never used, twelve-packs of an energy drink I'd never seen him touch, alibi groceries to make the trips look real. I noticed the membership renewal hit our account twice.

Then, on a Thursday, I drove there myself. I parked at the far end and sat with the engine ticking. I told myself I was being insane. I told myself I'd buy the loo roll and laugh about this someday.

I found them near the freezer aisle, in the white cold light, standing closer than two people pushing the same empty cart ever stand. He was laughing at something. He had not laughed like that in our kitchen in two years.

He never saw me. I left the cart where it was and walked back out into the ordinary dark of the parking lot, and I understood, fully and finally, that the most insulting thing about the whole affair was the setting. He'd given her warehouse walks. He'd given me a renewal fee.