He talks in his sleep, but I never thought he'd confess in it.

It started as the dumbest argument two people can have. I said he snored. He swore he didn't, said it was me, that I sounded like a chainsaw with a head cold. So one night he laughed, pulled out his phone, and downloaded one of those sleep-tracking apps that records noise while you're out. "Fine," he said, propping the phone on the nightstand like a tiny referee. "We'll let science decide."

Science decided he snored. We laughed about the graph the next morning, the little red mountains where he'd rumbled at two a.m. He kept the app, mostly out of vanity, swearing he'd train himself out of it. For three weeks it was a joke between us, a thing we checked over coffee.

Then there was a Tuesday when he left for work early and forgot to clear the night's recording. I was lying in bed with nowhere to be, scrolling, and I thought, idly, that I'd never actually heard what I sound like asleep. I opened the app. I tapped the timeline at random, somewhere around three in the morning, expecting snores or that embarrassing mouth-breathing everyone does.

What I heard was his voice. Soft, slurred, half-formed the way sleep makes words, but unmistakable. He was talking. Not nonsense. Not the gibberish people mumble in dreams. He was having a conversation with someone who wasn't there, and he was being tender.

He said her name. Felix. He said it the way you say a name you've worn smooth from saying. "Felix, don't—" and then something I couldn't catch, and then a low laugh, the private kind, the kind he used to laugh into my hair. "I know. I know. I'll tell her." A pause, his breathing. "Just give me time."

I sat very still. I told myself it was a dream, that dreams pull names from anywhere, that Felix was just someone from his office, a coworker, that this meant nothing. I almost believed it. I scrubbed back and listened again. Then I scrubbed forward, into the next clip, and the one after that, and across four nights of recordings my sleeping boyfriend told me everything his waking mouth had spent months hiding.

Some of it was domestic and that was the part that broke me. "I made you that playlist." "Did you eat?" "Tell me about your day." The ordinary little intimacies, the maintenance of a real relationship, conducted in his unconscious while I slept eight inches away. He had two lives, and he was running the second one in his sleep because there was no room for it anywhere else.

I didn't scream. I didn't throw the phone. I got up, made tea I didn't drink, and waited for the thing I needed, which was proof he couldn't blame on a dream.

His phone passcode was my birthday. That detail still makes me laugh in an ugly way. The messages were there, under a contact saved as a man's name with no last name, and the moment I opened the thread I recognized the cadence from the recordings. The playlist he mentioned. The "did you eat." Felix was a she, a woman from his work, and they had been doing this since the spring. The texts from the night before lined up almost word for word with what he'd murmured at three a.m. He had told me he was going to tell me. He'd promised it to her in his sleep. He just never got around to telling me while awake.

I took screenshots of everything. Then I emailed the audio files to myself, because some cold practical part of me knew I'd want to be sure later, on the days I'd try to convince myself I'd imagined it.

When he got home I was sitting at the kitchen table with the phone face-up between us, the app open to the night's red mountains. I pressed play. I watched his face change as his own sleeping voice filled the room, saying her name, soft as a prayer. He went grey. He opened his mouth and I held up my hand because I genuinely could not bear to hear the waking version of him lie when I had four nights of the honest one.

"You already told me," I said. "You just didn't know I was listening."

He moved out that weekend. He kept apologizing, kept saying it had gotten away from him, as if it were weather. Maybe it had. The cruelest thing wasn't even the affair. It was learning that somewhere underneath all his careful daytime love, his truest self had been quietly choosing someone else, night after night, while I slept trusting beside him.

I deleted the app. But I kept the files. Not to torture myself. To remember that I didn't make it up, that my body had been right to feel the cold spot in the bed long before my mind would let me name it.

He snored, by the way. The graph never lied. Turns out neither did he, once he was asleep.