I used to receive messages like this from my ex-boyfriend: “Did we have a joke about flamingos?” And: “How did I get the scar on my hand?”

They weren’t invitations for a trip down memory lane; he was asking because he couldn’t remember.

“We liked flamingos for their flamboyance,” I said. “The scar is from when you dropped a scalpel in your studio.”

I wasn’t just his ex-girlfriend; I had become the sole repository of our shared memories.

I met Sam in London when he was 20 and I was 24. After three years, I felt him drifting away. We went to the pub, ordered a bottle of prosecco and toasted our time together. We knew when the bottle was finished, we would say goodbye; we cried as we reached the last drop.

“Everything I know about myself has come through you,” he said. “I don’t know who I am without you.”

“That’s probably why we have to break up,” I said. “So you can figure that out.”

Six months later, Sam asked me out for coffee. We said we missed each other. It might have meant nothing, but I’ll never know, because a few days later a friend called to say that Sam had been in an accident.

After a night partying, he had fallen 25 feet from a tree and landed on concrete. Doctors induced a coma to prevent the swelling in his brain from causing a hemorrhage.

He and I had climbed a tree together on our first date. He was wearing Chelsea boots and I was in a miniskirt, but it didn’t matter. Tree climbing was part of the playfulness I loved about him. Now he might never climb a tree again. He might never wake up.

I used to kiss his closed eyelids and say, “I love your beautiful brain.” I imagined him in intensive care, that same brain swollen, perhaps beyond repair. I couldn’t rush to the hospital because I was just an ex, and I didn’t have a close relationship with his family. I could only send messages of support and wait.

A week later, his sister called to tell me the doctors had brought him around. “He asked for you,” she said, “I thought you’d broken up?”

When I arrived, Sam was sitting up in bed. I tried to see beyond the bandages and tubes, the metalwork bonding his bones. He was smiling.

We held hands. For a moment I thought it might be OK. Then he whispered, “I don’t know why I’m here?”

“You were in an accident,” I said, “but you’re safe now.”

Five minutes later, he asked again.

The head trauma had caused short-term memory loss, significant enough that several times Sam tried to get out of bed in confusion and fell. His mind would restart every few minutes, causing a stream of kaleidoscopic ramblings. He was still eloquent and charming in his incoherence, as if trying to talk his way out of the abyss of amnesia. He greeted each nurse as if they were visiting for tea.

I soon realized it wasn’t just his short-term memory. He didn’t know he was about to start a graduate program at the Central Saint Martins or that he lived in a dilapidated warehouse in Whitechapel with a pet rabbit. His childhood was intact, but the last few years — the span of our entire relationship — had vanished.

He knew who I was but couldn’t remember what I did or how we met. He couldn’t have recalled, for example, that first tree-climbing date, or how the next morning he went to buy us breakfast and returned with three boxes of cake from a French patisserie, and we ate strawberry cream puffs naked in bed with our bare hands.

He couldn’t remember our strolls down Brick Lane in our Sunday best or dancing in a field with our friends. He couldn’t remember the joy. And if he couldn’t remember the joy, it may as well have never happened.

To break up with someone is to lose the imagined future you would create together, but you would always share the landscape of your collective past. If Sam could not remember, I would be alone in that landscape.

I left that first visit shaking.

His doctor said we had a window of opportunity to restore his memories and the more we could help him recall now the less permanent damage might be. I visited most weeks. So did his closest friends.

As Sam struggled through his recovery, I turned up with slide shows. Sam in the catacombs of Paris on our first trip together. Sam with the 18th-century calvary sword I gave him for his 21st birthday. I showed him pictures of our mutual friends. Sam cried with delight, as if a switch in his brain had flicked on and let the light flood in.

I soon realized that as much as he didn’t remember our time together, he also didn’t remember that we had broken up. To Sam, I was still his girlfriend. On subsequent visits, I kept intending to tell him the truth and then didn’t. His short-term memory remained patchy, which I used as an excuse. And I enjoyed our hours together, sharing with pleasure memories that after our breakup had been so painful.

I was also trying to be careful. I didn’t want my telling of our story to influence his own burgeoning memories. Part of the pleasure — and conflict — in collective reminiscence is the inevitable discrepancies. I yearned for those discrepancies. I wanted an account of our story to exist independent to mine, but there was little I could do to prevent my account of our past polluting his own.

As an undergraduate, Sam studied neuroscience. In his proper mind, he would find what was happening to him fascinating. His brain was busy threading its neural networks back together, triggering those patterns of synaptic activity that make up a memory, and in doing so slowly restoring his sense of self. Our memories make us who we are. They are the connective tissue not only between our past and present selves but between us and the people we love.

About a month into his recovery, Sam said he wanted to talk. He had asked a friend why I didn’t visit more often, and this friend had said we were no longer together.

Sam asked me what happened.

“You fell out of love with me,” I said.

“Why?”

I didn’t know. That was the point in our story where his experience branched away from mine. “You were ready to move on,” I said.

“I feel like I have to go through the emotions of breaking up all over again,” he said.

Cycling home, I realized I did too. In the process of telling Sam stories about our past, I had created a new story, and it ended with us getting back together. I had let myself daydream about that Hollywood ending without stopping to question whether it was what either of us would want.

After five months, Sam was discharged. He had a slight limp and a toolbox of metal in his bones, but he walked out on his own with his beautiful brain intact.

We hadn’t talked about our relationship after that conversation, but he had become an important part of my life again. One night, only a few weeks after his release, I was at a party when a friend said, “It must be really hard now that Sam has a new girlfriend.” I left in tears.

I texted to tell him I didn’t want to see him for a while. I didn’t give an explanation.

“I understand,” he said.

He had given me a pair of red gloves for my last birthday, a gift I had recognized as a sign of his waning affection. Previous gifts had included a hand-sewn cape and a painting he had spent weeks completing.

I went to the seaside, filled the red gloves with stones and hurled them in the sea. It was over.

A few months later, Sam asked me to meet. In a Soho cafe we had been to before, he said he was sorry and wanted me to know how important I was to him. I asked if he remembered the cafe. He said I had taken him there, and we had ordered five different cakes between us.

I smiled, relief washing through me. I realized I hadn’t spent those months visiting him to save our relationship, not really, no matter how romantic that ending had seemed. I wanted to save his memories of our relationship. Without a partner to the collective past, those memories became less real.

We create ourselves through the early relationships in our lives, as Sam had said when we broke up. And I wanted to be part of Sam’s story. I needed to know he remembered the joy. And he did.

Tyler Wetherall, a writer in Brooklyn, is the author of the memoir “No Way Home.”

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