I bought the camera because of a feeding schedule, of all things. Our cat, a fat orange tom named Biscuit, had been throwing up in the mornings, and the vet wanted to know whether he was gulping his food or stealing from the dog's bowl. So I ordered one of those little pet cameras, the kind that sits on a shelf and tosses treats if you tap a button on your phone. I told Daniel it was so we could spoil Biscuit from the office. He laughed and said I was turning into a crazy cat lady. I set it on the bookshelf in the living room, angled toward the food bowls, and forgot about it for weeks.

I worked in billing for a dental group, the kind of job where the afternoons crawl. On slow days I would open the app and watch Biscuit sleep in the square of sun on the rug. It became a small comfort, a window into the quiet of my own home while I sat under fluorescent lights chasing down unpaid claims. I would whisper to him through my phone, even though he couldn't hear me, and the dog would lift his head at nothing.

That Tuesday started like any other. Around two o'clock I opened the app expecting Biscuit on the rug. He wasn't there. The rug was empty, the sun had moved, and the living room looked subtly wrong, the way a room looks when someone has been moving through it. Then a woman walked into frame.

I didn't know her. I want to be clear about that, because for the first few seconds my brain insisted I must. She was younger than me, in leggings and one of Daniel's old gray T-shirts, the one with the faded logo from his college. She walked through my living room with the loose, barefoot ease of someone who had been there before, who knew where the kitchen was without looking. She set a glass down on my coffee table without a coaster.

I remember thinking, absurdly, about the coaster.

Biscuit wandered into the shot then, tail up, doing his hopeful figure-eight around her ankles the way he did with everyone. And she looked down at him, and she nudged him out of her way with the side of her foot. Not gently. A small, irritated little kick, the kind you give a thing that is in your path. He scampered off. She didn't even watch him go.

That was the moment something in my chest went very cold and very still. Not the T-shirt, not the bare feet, not the glass. The kick. Because in that one careless motion I understood everything about how little this woman cared for the life Daniel and I had built. She was not a guest. A guest is kind to the cat. She moved through my home like it was a hotel room she had no intention of remembering.

I sat at my desk with my headset still on and a claim half-typed on the screen, and I watched. She drifted out of frame toward the bedroom. Daniel walked through a minute later in his work shirt, no tie, and he didn't look at the camera, didn't know it could see him, and he followed her down the hall like it was the most ordinary afternoon of his life.

I had told him I had a late meeting. I didn't. The meeting had been cancelled at lunch. I had simply been too tired to text him, planning to surprise myself with an early evening at home. He had clearly planned the opposite.

I don't know how long I stared at the empty living room after that. A coworker asked if I was okay and I said the words "stomach bug" and gathered my bag and walked out into a parking lot that felt too bright. I didn't drive home. I sat in my car and watched the feed loop in my mind, the foot, the cat, the glass with no coaster, and I let myself understand that the marriage I thought I had was a set he struck the moment I left for work.

When I finally went home that night the glass was washed and back in the cupboard. The T-shirt was in the hamper, turned inside out. Biscuit met me at the door, and I picked him up and held him longer than he wanted, and he forgave me for it the way cats do.

I never told Daniel how I knew. I let him build a careful story over the next week, and I let it collapse under its own weight, and when I finally laid it all out he kept asking the same useless question: how, how could I possibly know. I never gave him the camera. Some part of me wanted to keep one thing he couldn't explain his way out of.

I kept the camera, too, when I left. It still sits on a shelf in my new apartment, angled at a food bowl, watching a fat orange cat sleep in a square of afternoon sun. It only ever shows me what is actually there. I have learned to be grateful for that.