One Sunday I came to sit with the dead. The room was almost untouched. Everything and nothing was the same. I was standing in my grandmother’s study. She had lived with us for 25 years, and died six months earlier. Her room had been cleaned and closed – the dark beetles of dried blood scrubbed from the fireplace where she fell and cracked her head. I had come to her room to sit with the silence.

I have always found something deeply compelling about keeping quiet. It began when my grandmother moved in with us, when I was a child. Or at the edge of being a child: 13. The move shifted the family dynamic. It was a time of great upheaval, and it was during this time that I lost the ability to speak. Or not to speak, precisely, but to speak in the ways that make us human. The ways that matter. I could answer direct questions. I could take part in school plays. But I stopped making conversation for nearly a year. When I was at school, I stopped telling jokes, or asking questions. I became a lurker – always almost invisible, on the edge of conversations.

When my grandmother moved in with us there was a corrosion: of privacy, space and time, which meant not everything was spoken. I wanted to try to compensate for some of the things unsaid. “I’m getting married,” I whispered to the listening room.

I never told my grandmother I had got engaged. My parents admired my new engagement ring as we sat beside her hospital bed. I wish she had known. But I never found the words to tell her that I was marrying a woman – perhaps fearing her understanding of a wedding was not elastic enough to contain two brides at the altar. In the years since I had come out she had come to develop a simultaneous soft spot for my girlfriend and utter horror of the idea of our sexual intimacy. So there was always something unspoken. I couldn’t blame her. I only gave voice to my sexuality when I was in my 30s. And even then I could barely say the words: “lesbian”, “dyke” and “bisexuality” sounded like a medical condition, so I simply muttered “I like women” to anyone who would listen. I think I hoped that if I said it enough times I could banish the shame and doubt that made it impossible to articulate.

It was shame that seeded my early silence. And shame that kept my sexuality quiet for so long

I had come to my grandmother’s room to try to find something to read at the wedding. I scanned the shelves aimlessly, picking open old copies of Rupert Brooke, and anthologies of 20th-century love poetry. None of it was quite right. And then I saw it, an old book of mine, by George Oppen. A little known poet of the US west and east coasts. He prided himself on saying it as it was. On stripping everything back so that language could get as close as possible to the world. But at the same time his writing is incredibly sparse. It is almost as if he doesn’t want words to get in the way of the thing he is describing. The poems sit like little insects on the pages. Dots against the endless white.

I began to read, and my eye was drawn to one of the shorter poems. It was written about his wife Mary.

That this is I,

Not mine, which wakes

To where the present

Sun pours in the present, to the air perhaps

Of love and of

Conviction.

I knew I had found it. That moment of bright optimism, and wanting to hold on to each other without taking ownership: “I, not mine”. These were the words I wanted to say.

That day in my grandmother’s study reignited my romance with Oppen. But as I reread his poetry on my way to and from work, I discovered that there was a silence at the heart of his writing. Between 1934 and 1962 he didn’t publish a word of poetry. His letters also stop abruptly in the 1930s, resuming decades later. During this silence, his life continued apace: he joined the Communist party before going to war, when he fought the advance of Hitler during the 40s, only to return, wounded, to the US, and fall under the suspicion of Senator McCarthy. And so he fled to Mexico, and lived as an exile for almost a decade, with his wife and daughter, before returning to the States in 1958. For all of this, there are no words. Or at least, there are no words written at the time. In the poetry and letters written in the later years of his life, Oppen begins to pick through everything that happened, sifting through and making sense of it all.

George Oppen didn’t write poetry for 28 years

I couldn’t understand Oppen’s silence – and why a poet hailed as a “serious craftsman” by Ezra Pound with “a sensibility not got out of other men’s books”, would stop writing for so long, only to win the Pulitzer once he started again, in 1968. I think perhaps I wanted to understand his silence so I could start to make sense of why I had stopped speaking, all those years ago.

Those silent years had been haunting me. As I sat in my grandmother’s study, I could see myself in the Volvo, on the long drive to secondary school, where silence first settled on me. It was a girls’ boarding school, and I was one of only three day girls in a year of nearly 100. From the start I felt like an outsider. For the first two weeks of term, the boarders were not permitted to call home. Instead, they wrote letters to their parents, and arrived in chapel red-eyed every morning. After this hiatus, they were allowed 10 minutes a week to use the public pay phone in the corridor.

Leaving school each evening became a guilty secret. I never announced when I was going, but slipped silently away. And I began to hide in the boot room during breakfast, waiting for a moment when I could slip into line unnoticed. Trunks and tuck boxes were stacked to the ceiling and the air smelt of sweat and linseed oil. No one was ever there for more than a few minutes – to collect a lacrosse stick or a textbook.

“Oh, hi,” they would say, “I didn’t see you there.”

“Yeah, sorry, I was just leaving,” I’d reply.

My days were bookended by awkward pauses, and as time went on the silence began to swell, until I found I had nothing to say. I never intended to stop talking – but soon keeping quiet became a habit. It felt safer, easier, somehow to say the bare minimum. I was never bullied – just ignored.

And then my father’s company had a reshuffle and he was made redundant. Silence closed over our house, and we were told not to tell anyone outside the family what was going on. In school the other girls went skiing and hung out on the Kings Road – no one else was living off credit cards and crossed fingers. “Blood runs thicker than water,” my mother had said, as she finished breakfast one morning, “and people don’t need to know about Daddy.”

I couldn’t find the words to tell my family what was happening at school; it seemed irrelevant in the face of their sadness. And at school, I knew not to talk about the sadness in our unheated house – so I didn’t. I took an involuntary step back from the world, and stopped telling anyone how I was feeling.

Oppen, too, stopped writing in a moment of crisis. For him, it was being confronted with the grinding poverty of the Great Depression. He had been travelling in France, setting up a publishing house with his new wife, and living off his inheritance. But he returned to the US to find snaking soup kitchen lines, of men with nothing to eat. Fifteen million families were faced with the threat of imminent starvation, and, by 1934, 20 million people were unemployed. The previously self-assured young poet was at a loss. How could he write when all around him families were struggling to survive?

These were real, ethical questions for Oppen. In his one published essay on the purpose of poetry, The Mind’s Own Place, he recalls the words of the dramatist Bertolt Brecht, who believed that there were times when “it can be almost a crime to write of trees”. There are, Oppen argued, situations “that cannot honourably be met by art”. Poetry was not an appropriate response to starvation. And so he and his wife Mary took up politics with a view to creating “disorder, disorder – to make it impossible to allow people to starve”.

There was a power in choosing not to speak during this time. Oppen explained his silence as a way of preventing his words from being used in the service of the communist propaganda machine. And yet, there was more to his silence: shame. He came from a wealthy Jewish background, and told one correspondent he was “born of a couple of rather millionaire lines”, and it seems to me that part of his reluctance to write about the Depression is because of this inheritance. His moneyed childhood was at odds with his life as a communist agitator in the 1930s. And so there was always something he held back. An element of his life that remained unsaid. As Mary admitted, in a later interview, the couple’s financial security was the “guilty secret”, that allowed them to risk arrest on a picket line – as nothing mattered quite as much when you had money.

It was shame, too, that seeded my early silence. And shame that kept my sexuality quiet for so long, obscured even from myself. Perhaps it was only in getting married – standing up and saying “this is who I am” – that I really made peace with everything that had that had gone before.

The irony is I can’t remember most of what we said during the ceremony. We had not written our own vows, preferring instead the ones they give out at the register office; a laminated piece of paper passed from hand to hand. We wanted to participate in a ritual bigger than our own made up promises. So the words were demotic. Spoken. Not written. The moments I remember are more physical; the registrar asking us to hold hands – and being transported back to our second date, and the way our fingertips had touched, which was the first physical intimation that I had been right, and all the telling and retelling had been worth it.

The words I remember from the day are Oppen’s; the poet who always endeavoured to write poetry that was truthful, and who, in the end, emerged from silence because he believed poetry had a duty to bear witness to the world. For us, he bore witness to the bright certainty of love – “That this is I, not mine” – and the hope that from now on things would be different.

• Unspeakable: The Things We Cannot Say by Harriet Shawcross is published by Canongate on 7 March.