A queen-size bed can sleep two adult men comfortably. It can fit three if you don’t mind cuddling — or waking up to strange noises in the dark.

One early July morning, I opened my eyes to my boyfriend making out with the guy who had been living with us for the past month. Not really a fan of sex before tooth-brushing, I smiled, mumbled “hot” and turned over.

This had become our sleeping arrangement that summer: my boyfriend, our new lover and me. Add our Chihuahua at the foot of the bed and it was a tight squeeze. It’s a miracle we weren’t sleep deprived. In fact, we felt the opposite. After six turbulent years together, my boyfriend and I were falling in love all over again. Not with each other, exactly, but with this Third.

Long before meeting the Third, our relationship had downgraded into reruns of the same drama, our fights rehearsed through years of repetition. But now we had a guest star. With a new script in our hands, we wondered, could this be our comeback?

My boyfriend and I met on a blind date in Washington D.C. when I was a college sophomore. He was tall, smart, handsome, a few years older and he laughed at my jokes. He fit the bill and he paid it too. The next morning, I told my roommate, “I think he’s the one,” (which was, admittedly, deranged). By the end of the month, we were spending every night together.

It was both my and his first relationship, so we stumbled through various firsts together: first fight, first “I love you,” first meet-the-parents, and, after a year and half, first infidelity. We tried to break up, but the intensity (or insanity) of our love was addictive. I spent many nights crying performatively in the library before calling him back.

After graduation, I was determined to move to Los Angeles and become a filmmaker. This plan had several holes. For one, it did not account for my boyfriend. With all the deluded confidence of a college senior, I saw no issue. My undergrad era was ending, and now real life would begin. He was not pleased.

We tried to break up again but drove across the country together instead — he to San Francisco for law school and I to the city of angels. Resettled on the West Coast, we tried to break up yet again. He wanted commitment; I wanted space. We spent a year apart, but when he accepted a summer internship in Los Angeles (coincidence?), we decided to give it another go.

By the fall, he had transferred to U.C.L.A., and we had signed a one-bedroom lease together in West Hollywood. We adopted a dog. We bickered in Ikea. We opened the relationship.

It was important to me that we reject all heteronormative structures (read: I wanted to sleep with other people) and my boyfriend begrudgingly acquiesced. Despite our new arrangement, we were in many ways the same couple, just older and maybe a bit tanner.

Enter the Third. It was a sweaty June day and we were at a pool party for the gay dating app I work for. Go-go dancers gyrated by the D.J. booth, more than a few of my co-workers wore Speedos and the open bar was strong. The mood was set for love.

My co-worker introduced me to his friend from the East Coast who was interning at a Los Angeles TV network for the summer. The friend had me take his picture on a swan-shaped pool floaty (did I mention we were gay?). I thought there was something special about the way he held my gaze. Well that, and he was adorable. My boyfriend agreed. That night, he came home with us.

We had tried threesomes before, but rarely successfully, and never with a repeat player. I had always found the experience to be a dangerous balancing act in performing equal desire for both my partner and the newcomer. It was challenging theater that took me so deep inside my own head that I was incapable of being present.

But with this guy, it was different. In a rare feat of sexual chemistry, no one was left out.

Before long, he was spending every night with us. My boyfriend would drive him to his internship in the mornings and we would reunite in the evenings for dinner. On the weekends, we would take spin classes together, swim in the Pacific, eat ice cream, dance at warehouse parties. With all his youthful energy and optimism, the Third had resuscitated our joie de vivre. This was our summer of love.

The rules were loosely defined, which is to say, there were none. My boyfriend and I didn’t discuss what was happening, other than a breathless, “Isn’t this incredible?” We knew the Third’s internship would end in August regardless, so why fret? There was no time to waste.

In mid-July, I realized we were falling in love. We were at a tapas restaurant downtown and the Third was telling a story from his childhood. I looked over to see my boyfriend smiling and staring intently at him. His expression was so smitten that for a moment I wanted to smack his grin away, thinking, “You don’t look at me like that anymore.” But then I blinked and realized that I was wearing the same, doofy expression.

We were both committing the same crime at the same time, so all would be forgiven, right?

Not quite. When our group chat fell silent one afternoon while they were together, I found myself running home from work early in hopes of catching them “at it.” I never did, but I began to resent their solo drives to work together. I started checking the live video feed from our dog’s treat dispenser in the living room. Jealousy was rearing its heinous little head, made even more grotesque by the guilt of knowing that I, too, craved solo time with the Third.

The geometry of a throuple is complex. With a couple, there’s only a straight line connecting two dots. But introduce a third point, and so many more possibilities emerge — only one of which is an equilateral triangle.

Although the Third slept between us in bed, sat across from us at dinner and walked between us holding both of our hands, the angles in our throuple kept shifting.

One afternoon, I discovered that my boyfriend had bought the Third a new pair of cycling shoes. It was a shallow cut, sure, but it proved, for me, a shared impulse to reel the Third closer to our own respective sides of the triangle. Not to mention: Where were my shoes?

Gradually, our conflicts from seasons past started to replay themselves. By early August, our fighting escalated so much that we had to take things outside one night. “We’re embarrassing ourselves,” I said in a hiss. My boyfriend paced the sidewalk, steaming with rage, while I badgered him with questions. The nighttime dog walkers had stopped to stare by the time my boyfriend said, “He makes me feel the way you used to!”

It was one of those ugly sentences that slips out during a fight and shocks both parties with its precision. We both knew it was true, and I understood it completely because I felt the same way.

Summer ended. It was time for the Third to fly home. We dropped him off at the airport and exchanged tearful goodbyes not only to the throuple, but also, we must have known, to us as a couple. We turned onto the 405 in my boyfriend’s bright orange convertible and sobbed the whole way home.

The Third brought a light into the dark, dusty room of our relationship. That light woke us up, energized us, made us vulnerable again. But it also illuminated some boxes we had tried, for years, to keep tucked away. Boxes stuffed so full of resentments that they would make even a hoarder blush. Before the throuple, we could ignore our issues, file them away. But once we had a witness, we could no longer deny the evidence.

That August, we broke up, and this time it stuck. We were heartbroken thrice over, but we were changed. That final summer together reminded us how beautiful love could — and should — be.

After the breakup, I moved into a one-bedroom apartment. This time, I opted for a king-size bed, all to myself.

Sometimes I look at it and am embarrassed by its suggestion that I’ll be filling it with multiple lovers in various sexual choreographies. But most of the time, I spend my nights alone, sleeping smack dab in the middle. I sprawl.

Evan Sterrett is a writer and director in Los Angeles.

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