Just before bed one night, when I was eight, my mum told me she had a new boyfriend.

She seemed lighter than usual, excited even. But then she told me that Graham was married.

‘That means our relationship has to be kept secret,’ she said solemnly. ‘Promise not to tell anyone?’

I nodded, a slightly nervous feeling in my stomach. I had always been told not to lie, so this went against everything I had been taught.

But I adored my mum and wanted to do what she asked. I couldn’t have known how significant that moment would turn out to be for me, drawn into a world of deceit before I was old enough to comprehend it.

Understandably, there is rarely sympathy for the mistress in a story of infidelity, but I believe there should be more recognition for how children of the ‘other woman’ are impacted.

Certainly, it shaped me in fundamental ways, from how I saw men and relationships to bottling up my feelings to an unhealthy extent, and struggling with trust in my own marriage years later.

Mum was in her late 20s when she met Graham on a night out, three years after she split from my dad.

She had tried hard to make her marriage work but Dad was an alcoholic who could become violent when drunk. While I rarely saw him, I still loved him and cherished a silver cross he had bought me, which I kept in a blue velvet pouch.

Mum, meanwhile, worked hard so we didn’t go without, and she owned our house and the shop she worked in.

Soon after she told me about Graham, he came round one day.

I didn’t know what to expect but I was surprised by how smart he was, a well-off businessman dressed in a tweed blazer, shiny shoes and an expensive-looking watch.

I could see he was handsome but – a decade older than Mum – I thought he seemed a little dull for my fun, vivacious mother.

However, he was generous and money was no object. He always paid for holidays and showered Mum with jewellery.

He told me he didn’t have any children of his own but was very patient with me and would help with any tricky homework.

Graham would come over a few nights a week. Mum was so happy when he was around and I began looking forward to his visits, too.

He couldn’t take the place of my dad, but it was nice to have a father figure again.

I would get board games ready for us to play and draw pictures for him, even though he could never take them home.

A few months later, Mum and I spotted Graham and his wife in a supermarket.

Mum seemed shocked but I did as I was told, careful not to make eye contact with either of them. From a quick glance, I saw that his wife was beautiful.

To make sure we didn’t bump into them, it was almost as if we were playing a game of hide-and-seek around the aisles. It was exciting, but also felt wrong.

Life with Mum and Graham could be fun. We went to the Algarve and travelled around Britain in his sports car.

When Graham took us skiing in the French Alps, I was bursting to tell my friends how much fun I’d had, but I had to keep it to myself.

It wasn’t the kind of holiday Mum could afford, so I told people we had been to Spain instead. Mum loved the sun, so it sounded much more believable.

Looking back, I realise what a burden it was for a young child to carry these adult secrets. Unable to talk to anyone about what was happening, I began to internalise the idea that uncomfortable feelings were best kept to myself.

Clearly, Mum hoped that she and Graham would become an official couple. But three years into their affair, he told her he couldn’t leave his wife.

From my bedroom, I heard him say his wife had taken the news of him wanting to leave very badly, and he was worried about her mental health. But Mum was just as distraught. I heard her in hysterics and watched as she ran out into the street after him, howling.

Although I didn’t fully understand what was happening, I began to cry too. Mums were supposed to be strong and it was horrible seeing her like this. I also felt sad because I’d grown to like Graham and see him as a stepdad.

Mum struggled in the aftermath. She began having panic attacks and they were so terrifying I thought she was dying. Aged just 11, it was down to me to cheer her up, but I wasn’t sure how.

About a month later, I was arriving home from a school trip when I saw Mum looking out of the window as if she was waiting for me, still wearing her dressing gown. I knew something bad had happened.

When I stepped into the kitchen, she said, ‘Sophie, your dad has died.’

I burst into tears and we sobbed together. He was only 34, and Mum told me he had drunk himself to death.

But while I grieved, I found it difficult to speak about Dad with Mum, knowing how much he had hurt her in the past. It was another thing I had to keep to myself.

There was further drama to come. Within a few weeks, Mum and Graham were back together – and this time it appeared he had left his wife for good.

They bought a modest three-bedroom house in a different town, where nobody knew them. Meanwhile, I stayed with Mum’s sister and her family to finish the school term, visiting at weekends.

It felt as though Mum had prioritised her relationship with Graham over me, and I struggled with feelings of rejection, especially so soon after losing my dad.

It was a hellish time, when my own panic attacks – which would continue to plague me for decades, only stopping a few years ago – began.

Once the holidays started, I moved in with them and felt relieved that the affair was out in the open at least. The burden of keeping their secret was finally over.

But it wasn’t the fresh start Mum hoped for. Because, even though Graham said he loved her, he never committed to marrying her. And as the years passed, Mum told me that he was seeing other women, too.

I tried to persuade her to leave him, telling her she could have any man she wanted. I even wrote to Graham – who spent long periods away for work – to say he’d broken Mum’s heart and to leave her alone. He never replied or acknowledged it.

But he was all Mum wanted, and she eventually accepted an arrangement in which he supported her financially and promised not to leave her.

Graham’s wife – I don’t know if he ever actually divorced her – sent Mum hate mail, warning her that he would always be unfaithful, and Mum would read these letters to me.

Looking back, these were not appropriate things for a mother to be sharing with her 14-year-old daughter. But Mum needed someone to share the pain and humiliation of her relationship with – and that person became me.

Our lives revolved around whether Graham was around or absent. He preferred Mum not to work, so she would be free to go on holiday with him.

It was around this time that Mum handed me an envelope on which she’d written: ‘To Sophie, Not to be opened until my death.’

I was confused – Mum was only 36, hardly old – but all she told me was to keep it somewhere safe.

By then, I was so used to keeping Mum’s secrets that it never occurred to me to open the envelope before I was supposed to. Bemused, I tucked it away in my diary.

Only now do I realise what a burden it was to be given something like that, planting the thought of losing Mum in my mind at an age when I should never have had to worry about such a thing.

All the while, Graham’s other affairs continued. Mum felt trapped, knowing that she would be left with nothing if they separated. I also felt that she couldn’t bear the thought of Graham’s wife being proved right.

But I watched how his lies and betrayals diminished her. She went from vibrant and sociable to thin and increasingly withdrawn, eventually becoming almost reclusive.

At 15, I began having suicidal thoughts. I was still grieving my father and struggling with everything I had kept bottled up since I was eight. Mum didn’t notice anything amiss, too caught up in her relationship troubles.

So, without telling anyone, I made an appointment to see the doctor. I broke down in front of the GP, who prescribed me antidepressants.

Days later, Mum found the tablets hidden under some drawers and was furious. She told me I didn’t know what depression was. I knew she was suffering, but I needed help, too.

I went straight into work after leaving school, ending up in retail working for a clothing brand.

When I was 22, I secured a transfer from our home in the North of England to one of the company’s London stores. I was excited to start a new adventure. I needed space to discover who I was.

Moving into head-office roles I grew in confidence professionally, though I lacked confidence when it came to men. As a result of my childhood, I didn’t trust that they wouldn’t betray me.

But then I fell in love with a guitarist with a big personality, and we got engaged.

At 28, we had a son together. But after his birth, I suffered from postnatal depression and Mum urged me to come home. In the end, I returned north as a single mum with a two-year-old, and it was wonderful seeing Mum so happy to spend time with us.

Graham was still on the scene, too, though was still unreliable.

Within a few months, determined not to give up on love, I signed up to a dating website and met David, then 31, an electrician. He had recently come out of a long-term relationship and, like me, had a son, then seven.

We chatted online for a few weeks before meeting in person and, from that moment, were inseparable.

I was open with David about everything I had been through from the start. He was shocked that I had endured so much yet seemed, as he put it, quite ‘normal’.

I loved that he had grown up with siblings and parents who had been married for 33 years, and who seemed to have no secrets between them.

Fourteen months later, David proposed at midnight on Christmas Eve, hiding an antique engagement ring inside a cracker.

I had never been so happy. I was 31, had my little boy, a fiancé I loved and a wedding to look forward to.

But just seven days later, on New Year’s Eve 2012, Graham – who by then had been in a relationship with Mum for 23 years – knocked on my door looking broken, with a police car parked outside. ‘Your mum has killed herself,’ he said. She was just 53.

I was absolutely devastated. While she hadn’t seemed happy for a long time, I never thought she would take her own life, especially as she adored my son and was excited about my engagement. I’ll never know if there was a final catalyst that sparked her decision.

The next day, New Year’s Day, I remembered her letter, to be opened upon her death, and finally opened it:

My Darling Sophie . . .

When the time comes for you to meet the man of your life, learn by my mistakes and make sure he is the right one. Don’t let men take advantage of you. Find someone who absolutely adores you and loves you so much it hurts. It has to be 100 per cent or nothing.

Knowing that she had written those words almost two decades earlier, when she was only 36, was heartbreaking.

While she had not handled some aspects of my childhood well, she was still my mother and I loved her. And she wanted me to have the kind of love she had never found herself.

In the months that followed, I had grief counselling – the first time I had ever opened up to a professional. It was such a release to let out the emotions I had kept bottled up for so many years.

There were plenty of tears, not only for the loss of Mum but for Dad too. We spoke about how difficult it can be to feel truly secure when you have experienced people you love hiding the truth and telling lies.

I was so grateful to have David’s support too and we married in June 2014. But my brain wouldn’t let me accept that I had found my happy ever after.

Mum’s letter stayed with me. She meant well, but I found myself asking David the right man for me?

For a while, I became convinced that he must be having an affair. After all, growing up watching Mum and Graham, I had been raised to believe people would betray you.

But David remained steadfast, and transparent about everything he did, and told me I had to learn that not everyone acted the way Graham had.

Through grief, time and support, Mum’s letter made me realise that I had, in fact, found my person. David had seen me at my lowest – but through it all he stood by me.

In fact, I’m not sure how I would have coped with everything that followed without him.

Now 45, I’ve started writing my memoir, My Darling Sophie, because I want my son, who is now 17, to understand more about me and the grandparents he never had the chance to know.

When I think about my son when he was aged eight, I can’t imagine asking him to keep a secret like my mother did.

He was so little and it makes me realise just how much I was asked to take on at an age when I should have been allowed to be a child.

I have compassion for Mum, who had been through so much and was chasing her own happy ending. Ultimately, I feel more blame for everything that happened lies with Graham, so I don’t resent Mum. I just wish she had realised what she was asking me to carry and, later, that I needed emotional support, too.

I want my son to know that he can tell me anything. I never want him to feel that his pain doesn’t count because someone else is going through something worse.

Today, Mum’s ashes sit in a ceramic case in my dressing room, alongside a bottle of her favourite Dior perfume. I’m not sure I will ever feel ready to let her go.

As for Graham, I last had contact with him in 2017, and have no wish ever to speak to him again.

More important is what I have to look forward to. I have my son, David, a family, a career in the design industry that I love, and happiness. I was burdened with secrets I should never have been asked to keep, but I won’t let them define me.

Graham’s name has been changed.

For confidential support call the Samaritans for free on 116 123 or go to samaritans.org.

As told to Julia Sidwell