The last thing my teacher asked of me, before I severed all ties, was that I respect her and her husband’s confidence as they’d respected mine.

My teacher and her husband had sexualised their pastoral relationship with me when I was at school. I was 15 when the relationship started, in my 20s before I was free of them.

When I’m asked to describe the relationship now, I find it difficult to make others understand. It was a bit like joining a cult. My teacher was a key mentor. I was thrilled to be invited to her house one weekend. Soon I was spending all my time with her and her husband. They were like parents – it felt like they were better than my real parents because they were so interested in me. Over time, I lost contact with friends my own age. There was only my teacher and her husband. And then the sexual contact started – first initiated by him, and then both of them.

It was just after I finished school that I became pregnant to my teacher’s husband. To protect them, I left my home town of Brisbane and went to St Joseph’s home for unwed mothers in Melbourne. I gave my baby, a girl I named Ruth, away for adoption.

For the next 20 years, I kept everything that had happened a secret, steeped in corrosive shame. I felt I’d caused harm to my teacher and her husband, not the other way round. I was like James Joyce’s Mr Duffy, living a short distance from my body. I never spoke of my experiences. I never thought of them. I became a writer but I didn’t write about what had happened.

It was not until years later, after I’d had a second, longed-for child, that my secrets came to the surface – that I knew, suddenly and viscerally, what leaving my daughter had meant. I’d hurt my tiny son accidentally, catching his skin in a stroller clip. Afterwards, I went into the bathroom and locked the door. My body began shaking violently, as if in fear. My legs would not stand me up. I fell to the floor, still shaking. I couldn’t speak, only moan. I had no idea what was happening.

Out it all came from there: the guilt of giving my child to strangers, the grief of losing baby Ruth, the terrible betrayal of my own childish trust. At first, I couldn’t write anything. The friends I’d made after I left my teacher and her husband, and especially the gentle man I’d married, saved my life more than once. I had a string of therapists who helped, mind, body and soul. My body continued to lead the way.

At some stage during this period, I was asked by the Australian Taxation Office to explain why they shouldn’t have issued me a fine for submitting GST information late. It hadn’t advantaged me to submit late, but I was barely managing to meet my work commitments during that time, let alone manage the usual adult administrative responsibilities. Some days, I did not feel my life would go on. I was surviving.

I wrote a letter to the commissioner for taxation. I explained that a past grief had overwhelmed me. It was such a seemingly perfunctory thing – explaining to the tax office why I had filed information late – but this was the first time I had told anyone in authority something about what had happened to me. It was a beginning.

The deputy commissioner wrote back. On this occasion, they would allow my appeal, she said. I should make sure I got my tax information done on time in future.

I don’t always get my tax information in on time, but the deputy commissioner’s letter was the first experience I had of someone in any formal capacity acknowledging what had happened to me. I can’t tell you how healing it was. It can still bring me to tears.

This is why the work of the royal commission into institutional responses to child sexual abuse is important. Many institutions, religious and secular, failed children much younger than I was, and much more catastrophically than I was failed. These institutions are failing still. The royal commission is doing the work of making them acknowledge their failures, creating a space where secret shame can be washed away.

Over time, I have been freed of my secrets, and I have let go of shame.

Toni Morrison said the function of freedom is to free someone else. Anne Lamott tells us that if we are no longer racked or in bondage to a person or a way of life, we must tell our story. We must risk freeing someone else. “Not everyone will be glad you did,” she says. “What are you going to do?”

I wrote For a Girl.

• For A Girl: A True Story of Secrets, Motherhood and Hope by Mary-Rose MacColl is out now through Allen and Unwin