In the box, an old envelope, a Brooklyn address penned carefully in black ink. Inside the envelope is a birthday card. For which birthday, I no longer remember. I remember only the gist of what it says. I'm grateful for your birth or something along those lines. Even if we never speak again. The envelope is sealed, the glue a decade old. The front stamped: RETURN TO SENDER, RECIPIENT UNKNOWN. The day I received that card in the mail was the day I knew I had officially lost you.

For months after we parted, whenever I found myself in Brooklyn, walking along cobblestone streets or through lines of unfamiliar brownstones, I wondered how close I was to you. I wondered if my hands grazed railings you had touched, if the air I breathed was comprised of molecules left in your wake. I imagined my feet crossing paths you had taken, my palms cupping doorknobs smudged with your fingerprints. Each possibility, a breadcrumb, a pebble, left by you to lead me back to your side.

I collected the things you had given me — the glittered birthday cards, a stuffed frog, a plastic yellow keychain shaped like a key, a postcard of an ugly dog, post-it notes you left on my computer screen — and hid them in a shoebox. I put in our photographs, the letters I never sent you, ticket stubs and playbills, and closed the lid. I do not know if I was putting them there to keep them safe, or to keep them hidden. I suppose it was both. Things I could neither part with nor bear to look at.

Even after the card was returned, I dreamt of running into you. I imagined a night scene, a narrow street in Manhattan, trash bags lining the sidewalks. I imagined seeing you in a dark winter coat, your hands shoved into pockets, registering me first with surprise, then joy. I imagined what I would say. Wow, fancy running into you here! or Long time! Perhaps we should grab coffee? or Of all the sidewalks, in all the towns, in all the world… I wondered if you missed me the way I missed you. I wondered if I entered your dreams as often and infuriatingly as you entered mine.

Time passed and I changed. I quit my job as a publicity assistant to go back to school for graphic design. I made new friends and switched lipstick shades and took up photography. I went to weddings. I went on blind dates. I developed a taste for bourbon. I learned to snowboard. I drank more before I drank less. I grew up.

When social media happened, when you added me on MySpace, then later Facebook, I messaged you carefully, trying to exude friendliness without being overeager. Hey, I said. It's great to hear from you! Maybe we could meet up sometime. You never wrote back. Instead, I began to see pictures of her: hair messy on a windy sidewalk, sun-dazed in a striped bikini, hovering over a home-cooked meal. I wondered if she knew that runny eggs make you gag, that Casablanca makes you cry, that you're most ticklish on the inside of your elbows, that once upon a time you couldn't fall asleep without the radio on. I wondered if our secrets were now her secrets too.

A few more years went by. My friends who were married were getting divorced, and my friends who were single were getting married. Somewhere in between, babies were born. Other people were putting out first films, first books, first IPOs. I fell in and out of relationships, sometimes relieved, often broken. When each one ended, I opened up your shoebox. I read through our notes. I thumbed through our pictures. I picked out the card you'd never read and held it up to the light. I contemplated opening the envelope.

Tonight, your engagement photos populate my Facebook wall. I scroll through them, my stomach tight and aching. I see the way you gaze at her, and remember how once you cupped my face and held it in front of you, wanting to memorize me, For later. I see the way you kiss her forehead, your palm pushing her hair back, and remember how you used to make the same gesture to avoid the tickle of my bangs when I snuggled beneath your chin. I see the way you hold her hand gently, like it's precious, and remember how all my emails used to filter into a folder you labeled Precious.

But also I see the way she looks at you, like she has won the moon. I see the laughter you share, your eyes locked, the intimate joy hovering in the space between your bodies. I realize then — I do not know anything about you. I do not know the words you murmur in your sleep, nor the songs that make you want to dance. I do not know the way your hair smells at night nor the calluses on your hands. Once perhaps, but no longer. And finally I realize something I have always known, but couldn't accept — that you have not been mine for a long time.

I live in Brooklyn now, where I know you no longer do. The rain stipples the small skylight in my third floor walk-up, and I imagine you, somewhere across the country in a house I cannot picture, your arms around the woman who will be your wife. My imagination stops there. Your box is in my closet, the envelope sealed. I try to remember the words I wrote. My screen is blue. The rain pounds. I stare at your photos. The box still waits in my closet.