It started with the squeak of the flywheel at 1 a.m.

For years the spare-room bike had been a coat rack, a place to drape the laundry he swore he'd fold. Then, that spring, Daniel found religion in it. He clipped in before dawn. He clipped in after dinner. He clipped in at hours when the rest of the house was dark and the only sound in the walls was that thin metallic whir, steady as a pulse, drifting through the floorboards into our bedroom.

I told myself it was a good thing. He'd lost the soft middle he used to pinch in the mirror. He came to bed flushed and grinning, smelling of cold sweat and something almost like youth. A husband getting fit is not a husband to be suspicious of. That was the story I sold myself, right up until the night I couldn't sleep and pulled up his rider profile on my phone, just to see how far he'd gone.

The numbers were impressive. The little wall of activity beside them was not.

Every ride — every single one — was stamped with the same name cheering him on. A woman's handle, a sunflower beside it. While other riders collected a scattered handful of encouragements from strangers, Daniel collected hundreds, and they all came from her. Ride after ride, day after day, like a signature at the bottom of every page of his secret diary. Nobody fires off three hundred little bursts of applause at a stranger. That is not enthusiasm. That is a hand reaching across a dark room for another hand.

I tapped her profile. I expected an anonymous face in another city, easy to dismiss. Instead I found a woman who rode the same morning sessions I'd seen him sneak away for. I found a town listed under her name. Our town. I found a photo at a coffee shop two streets over, the one with the green awning where I buy the beans he likes.

She lived close enough to wave to. Maybe she had.

I sat on the edge of the tub with the bathroom fan roaring so he wouldn't hear me breathe, and I scrolled back through months of it. The timestamps told the rest. His midnight rides matched her midnight rides. They weren't exercising near each other by accident; they were meeting, in the only room of our house I'd been proud of, in plain sight, behind a wall of cartoon hands clapping. A flirtation so public it was practically broadcast, and I'd been the only person in our marriage too trusting to look.

The cruelest part wasn't the lie. It was the choreography of it — the way he'd kiss my forehead, say "going to ride," and pedal furiously toward another woman while I slept twenty feet away, lulled by the sound.

I didn't confront him that night. I went back to bed and lay listening to the flywheel spin down to silence, memorizing it, knowing it was the last time that sound would ever mean what I'd believed it meant.

In the morning, I unplugged the bike before he woke. He never asked why. He already knew I'd finally heard it.