In the 12th year of my marriage I began to write a novel, about a woman named Primrose whose life unravelled in the wake of her husband’s cancer battle. The story was about the wreckage left by the illness, about how two people united by a traumatic experience could somehow slip away from each other, become strangers under one roof.

The premise was inspired by my own story, as several years earlier my husband had found himself in a blood cancer ward, fighting for his life. The ward was a place where prognoses were delivered in hushed voices, where bags of chemo drugs arrived at the bedside, wearing Grim Reaper hoods to protect them from the light. People passed their days staring out of the seventh-floor windows as if they were floating away from the world. And in a sense, they were, because no one who entered the place came out quite the same.

That was true for both the patient and the carer. And, by the time my husband returned home, neither of us was the person the other married.

So, in the growing chasm left by the disease, in the 12th year of my marriage, art began to imitate life. I worked on the novel whenever I could. The relationship that spilled on to the page was one of tormented detachment, of a couple never quite getting to the heart of their heartache, always stepping around each other, keeping lies and secrets.

It made for good fiction but only to a point. At chapter 13 I came to a halt. The story had nowhere else to go. Primrose and her husband were irretrievably lost to each other and, despite my yearning for a happy ending, I could not will their marriage forward. In so far as art was imitating life, life seemed to have run out of material.

I began to think I needed to invent a third character to rescue Primrose out of her darkness. Then one day, in the shower, a thought came to me: a boy I’d known in high school, confident, independent, someone who walked to the beat of his own drum, never troubled by the opinions of others.

Despite being my polar opposite, this boy and I became friends. We bonded over the differences in our worldly views; we argued constantly about books and music and the theoretical possibilities of the universe.

After high school he’d drifted in and out of my life. He had graduated ahead of me and promptly disappeared to another state. Then he came back. In our early 20s we fell in love. But then he left again. He was always heading to another city, another country, in search of the right career path and the man he wanted to become.

As for me, I lingered in Melbourne, finished my law degree and landed a job that paid exorbitantly well but felt oddly depleting. Then I too was on the move, off to Sydney to start afresh as a journalist.

In all that time the opportunity was always there to forget him, to move on to another person within easier reach. But he had promised, and I had believed, that he would come back to me at the end of our wanderings.

I decided, as I stood in the shower, that this boy would cure my writer’s block. I would use him as the basis for a new character – Primrose’s first love who, by a twist of fate, would return to her 20 years later, just as her marriage was crumbling.

But that is not why I tell you this. I tell you because the boy was the one I eventually married, and he was the same person as the man who came to be in the cancer ward years later.

In trying to rescue my fiction, I had somehow reminded myself of what was real. The moment I remembered the boy, I realised why – no matter what our sorrows – I could never fall out of love with my husband.

It was the 12th year of our marriage but my 23rd year knowing him. And what I knew was his truest self, the innocent core of his being that could not be altered by age or circumstance, even tragedy.

• Nina Wan is the author of The Albatross, available now through Macmillan Australia

• Do you have a romantic realisation you would like to share? Email australia.lifestyle@theguardian.com with “The moment I knew” in the subject line to be considered for future columns