During my senior year of college, I dated a boy who was tall, dark-haired, and smoked a lot of weed. (If I’d had a checklist, those would have been the boxes on it at the time.)

We talked easily, about everything from medieval art to music, and I found his lanky limbs and soulful eyes very appealing. But despite how much we enjoyed each other’s company, both in bed and out of it, I didn’t, fundamentally, feel anything. If he’d told me he never wanted to speak to me again, I wouldn’t have cared, except that I’d have needed to get my weed from someone else.

That’s when I came up with the theory of the third thing.

The premise is that there are three things that make you fall for someone. The first is a physical connection. The second is an intellectual connection. And then there’s the third thing… whatever mysterious ingredient makes you imagine a future together. My friends and I spent hours sitting on the floor of my dorm room, listening to Matchbox 20 and drinking diet Snapple with vodka, trying to unravel what the third thing could be.

I was a good student. I was naturally shy and awkward, but I was also used to thinking things through and figuring them out. In middle school, I’d analysed my classmates’ social interactions, realising that when someone told a story about themselves, you were supposed to respond with a story on a similar topic.

In high school, I’d made a checklist of all the things I needed to do to be cool (start reading Seventeen magazine, stop walking around with a book in front of my face, keep gum in my backpack and offer it to my classmates after lunch).

In college, I’d turned my attention to boys. It was easy to kiss them on sticky bar dance floors and meet them for coffee dates at the student centre. But I wanted to fall in love, and I wasn’t sure how to do it. If I could figure out the third thing, then I’d know the formula. I’d know how to find someone who I was really excited about.

I dated regularly throughout my 20s, but nothing lasted. Then, following another breakup, I found myself spending a lot of time on the phone with my friend Dan. We’d dated briefly when we first met years before on study abroad. He was awkwardly, gawkily handsome, and was one of the smartest people I’d ever met, dropping references to Byzantine emperors into casual conversation. However, at that time, there just wasn’t that third thing.

Then, suddenly, eight years later, there was. I wasn’t sure what had changed. I still didn’t know what the third thing was, but something was different, even if I couldn’t identify it. For years we’d just been friends – albeit friends who drunkenly made out occasionally when we ended up in his car together late at night. And now we were spending all our time thinking about each other. How had this happened? And what were we going to do about it?

As it turned out, we were going to get married. Three years later, we found ourselves holding hands and saying vows in a historic library in Providence. We ate cupcakes, drank prosecco, and spent the night dancing with our friends and family among the stacks. It was the happiest day of my life; I’d found a smart, handsome man whom I loved, and who loved me. We had chemistry; we could spend hours talking, and most importantly, we had the third thing. I felt like I’d gotten exactly what I wanted.

Except that after 10 years of marriage, it wasn’t what I wanted anymore. Dan’s brooding moroseness, which I’d found appealing, had begun to seem whiny. My quest for self-improvement, which he’d found admirable, had begun to seem exhausting. It had started to drive me crazy that he sang to himself. It had started to drive him crazy that I left the cupboard doors open. These were things that we’d lived with for years. They hadn’t been a problem. And now, suddenly, they were, and I wasn’t sure why.

There were other, bigger issues. We were politically divided. We wanted to spend our time in very different ways. My marriage didn’t end just because we no longer had the third thing. But that was part of it. We were still attracted to each other. We still talked about everything as easily as we always had. But we no longer had that ineffable thing that made us feel romantic about each other.

We tried. We left our son with his grandparents over the 4th of July weekend, went to a local brewery for IPAs and pepperoni pizza, shared a joint and had sex in front of a mirror. We sat side by side, feeling miles away from each other, and watched fireworks explode into distant sparks of light. We went to two different couples’ therapists. They gave us worksheets. We did the worksheets. We still didn’t love each other anymore.

The hardest thing about the end of the marriage wasn’t the loss of the present. At the time, we were sleeping on separate floors of our old suburban house, trying not to touch when we passed each other in the stairway. But in my imagined future, we were going to be one of those elderly couples who travelled around the country in an RV, who went to see independent films and had season tickets to the local symphony. We were going to sit side by side at our son’s graduation, and when he crossed the stage, unimaginably tall but still wild-haired and bright-eyed, we were going to squeeze each other’s hands.

Instead, I was single and dating again in my 40s. From everything I knew about ageing while female, I figured that dating at that age would be some kind of barren wasteland. Instead, I discovered that the apps had come along and made it easy. I could go on a date with someone new every night if I wanted, and for a while I did. I was doing things I thought I’d never do again, like kissing strangers at the entrance to the subway. And for the first time, I was dating women, which was something I’d always wondered about. When I was younger, I’d gone from one man to another, and suddenly I wondered if maybe the reason I’d had trouble figuring out the third thing was that I didn’t want to be with a man. Maybe my newfound queerness held the answer I’d been seeking.

I started dating a beautiful woman with long blonde hair, tattoos and a sweet smile. We sent each other passages from books, we talked about theatre, we spent hours making out. Still, despite how much we enjoyed each other’s company, both in bed and out of it, there was no third thing. We were mutually unserious, and after a few months things came to an end.

I think someday I’d like to fall in love again, but I’m also terrified because I’m finally coming to understand that there isn’t a formula. I’m realising that the third thing is different at different times, or for different people. That it’s something that can appear out of nowhere… and can disappear, too. That sometimes love just goes away, and if I find it again, it might go away again, no matter how hard I try not to let that happen.

I’ve finally figured out that I might never figure it out. If the third thing comes my way again, it’s just going to be because I’m lucky. I can’t control whether I find it; I can only control whether I’m brave enough to say yes to it. I don’t know whether I will be.

For now, I write, I teach and I worry about the world, and I watch my son use Magna-Tiles to build rainbow castles reaching up towards the sky. Sometimes I swipe right on strangers, and meet them for hikes or cups of coffee. I walk my dog around the neighbourhood in the spring and watch the crabapples bursting into improbable, extravagant bloom. The flowers drift down from the trees as I walk underneath them. I reach out my hands to catch them, and I end up empty-handed, but later, when I get home, I find myself picking delicate pink petals out of my hair.

Lia Romeo is a playwright, essayist, novelist, and screenwriter. Her plays have been produced off-Broadway, as well as regionally and internationally, and her essays have appeared in the Washington Post, the New York Times, and other national publications. She is currently at work on a screenplay.

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