Laughing and dancing with my fiance at our engagement party, I thought I might actually burst with happiness.

Surrounded by our family and friends, I looked at Matthew and felt certain I had met the man I was going to spend the rest of my life with.

Quite simply, he was my soulmate.

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Karen Cross regrets leaving her first love and mistook contentment for unhappiness

We were desperately in love and had our future life together mapped out.

First we would save to buy our own home, then would come a romantic wedding ceremony and children would follow.

It all seemed so simple to my naïve, 19-year-old self. I was, I smugly told myself, the girl who had it all.

So why, 20 years later, do I find myself single, childless and tormented by the fact that I have thrown away the only true chance of happiness I ever had?

Happier times: Karen Cross with her former partner Matthew, who she thought was 'the one'

Eight years after that wonderful engagement party in 1989, I walked away from dear, devoted, loyal Matthew, convinced that somewhere out there, a better, more exciting, more fulfilling life awaited me.

Only there wasn't.

Now I am 42 and have all the trappings of success - a high-flying career, financial security and a home in the heart of London's trendy Notting Hill. But I don't have the one thing I crave more than anything: a loving husband and family.

'My father warned me not to throw this love away. But I was sure I'd find Mr Perfect around the corner'

You see, I never did find another man who offered everything Matthew did, who understood me and loved me like he did. Someone who was my best friend as well as my lover.

Today, seeing friends with their children around them tortures me, as I know I am unlikely ever to have a family of my own. I think about the times Matthew and I talked about having children, even discussing the names we would choose. I cannot believe I turned my back on so much happiness.Instead, here I am back on the singles market, looking for the very thing I discarded with barely a backward glance all those years ago.

I know I can't have Matthew back, and it hurts when I hear snippets of information about his life and how content he is. Fifteen years after I ended our relationship, he is happily married.

Karen met Matthew met when they were at school and started dating when she was 17

At this time of year, so many people will be assessing their lives and relationships, wondering if the grass is greener on the other side. Many will mistake contentment for boredom, forgetting to cherish the good things they have. I would urge those who are considering walking away from such riches to think again.

How different things would be for me now if only I'd listened to Matthew when he pleaded with me not to leave him in 1997, tears pouring down his face. I was crying too, and it tortured me to watch the heart of the man I loved breaking in front of me. But I was resolute.

Let's try again! Thirty-three per cent of adults said they’d reunite with their first love if they could, says one study

'One day I might look back and realise I've made the biggest mistake of my life,' I told him as we clung to each other desperately. How prophetic those words have proven to be.

'I will always be here for you,' Matthew promised. And I, arrogantly, thought that somehow I could put him on ice and return to him.

Matthew and I met when we attended the same comprehensive school in Essex. We started dating just before Christmas 1987 when I was 17 and studying for my A-levels. By that time he had left school and was working as a motorcycle courier.

We got on like a house on fire, and our families each supported the relationship. Before long, we had fallen in love. Matthew was romantic but incredibly practical, something that would later come to annoy me. His gifts to me that Christmas were a leather jacket - and a pair of thermal leggings.

While she still loved him, Karen began to feel embarrassed by Matthew's blue-collar jobs

Two weeks later, when we'd been seeing each other for less than a month, he proposed. We were in my little Mini Clubman when he shouted at me to stop the car. Scared something was wrong, I braked in the middle of traffic and we both jumped out.

Then, oblivious to the other drivers beeping their horns, he got down on one knee in the middle of the road. 'I love you, Karen Cross,' he said. 'Promise you'll marry me one day.' I laughed and said yes, thrilled that he felt the same way that I did.

In the summer of 1989, while out for a romantic meal, Matthew proposed properly with a diamond solitaire ring. Two months later, we held our engagement party for 40 friends and family at the little house we were renting at the time.

The following year, we bought a tiny starter home in Grays, Essex, which we moved into with furniture we had begged, borrowed and stolen. We giggled with delight at the thought of this grown-up new life.I was in my first junior role at a women's magazine and Matthew worked fitting tyres and exhausts, so our combined salaries of around £15,000 a year meant we struggled to make the mortgage payments. But we didn't care, telling ourselves that it wouldn't be long before we were earning more and able to afford weekly treats and a bigger home where we could bring up the babies we had planned.

But then, the housing market crashed and we were plunged into negative equity.

Struggling should have brought us closer together, and at first it did. But as time went on, and my magazine career - and salary - advanced, I started to resent Matthew as he drifted from one dead-end job to another.

Karen stopped appreciating little things he did, like leaving romantic notes on the pillow

I still loved him, but I began to feel embarrassed by his blue-collar jobs, annoyed that, despite his intelligence, he didn't have a career. Then he bought a lurid blue and pink VW Beetle.

Why couldn't he drive a normal car? Things that now seem incredibly insignificant began to niggle.

I began to wish he was more sophisticated and earned more. I felt envious of friends with better-off partners, who were able to support them as they started their families.

I stopped seeing Matthew as my equal. I stopped seeing all the qualities that had made me fall in love with him - his fierce intelligence, our shared sense of humour, his determination not to follow the crowd. Instead, I saw someone who was holding me back.

'I hated the fact Matthew was suddenly putting another woman before me. How dare she come between us! Over the next few weeks, I'm ashamed to say I vented my spleen at both of them in a series of heated phone calls'

I encouraged him to find a career and was thrilled when he was accepted to join the police in 1995. It should have heralded a new chapter in our lives, but it only hastened the end. We went from spending every evening and weekend together, to hardly seeing one another. Matthew was doing round-the-clock shifts, while I worked long hours on the launch of a new magazine.

Our sex life had dwindled and nights out together were rare. I stopped appreciating little things he did, like leaving romantic notes on the pillow or scouring secondhand bookshops for novels he knew I'd love. He was my best friend, yet I took him totally for granted.

After festering for weeks about his shortcomings, I told Matthew I was leaving. We spent hours talking and crying as he tried to convince me to stay, but I was adamant.

My parents were horrified that I was walking away from a man they felt was right for me. My father's words to me that day continue to haunt me. 'Karen, think carefully about what you're doing. There's a lot to be said for someone who truly loves you.'

'It's been 11 years since Matthew and I last spoke, I have to accept that door has closed' (posed by model)

But, I refused to listen, convinced there would be another, better Mr Right waiting around the corner.

I moved into a rented flat a few miles away in Hornchurch, Essex, and embraced single life with a vengeance. By now I was an editor on a national magazine. Life was one long round of premieres and dinner or drinks parties.

Matthew and I remained close, even telling each other about new relationships. But though I'd dumped him, I never felt the women he met were good enough. I can see now I was acting out of jealousy. I clearly wanted to keep him for myself.

Our closeness was, however, called to a halt in 2000 when he met his first serious girlfriend after me, Sara.

One night shortly after his 34th birthday, I phoned to ask his advice about something.

Matthew was unusually abrupt and asked me not to call him again. 'Please don't send me birthday or Christmas cards any more either. Sara opened your card last week and was really upset. I have to put her feelings first.'

I hated the fact Matthew was suddenly putting another woman before me. How dare she come between us! Over the next few weeks, I'm ashamed to say I vented my spleen at both of them in a series of heated phone calls.

I was completely irrational. I didn't want Matthew back, but felt upstaged by Sara.

Unsurprisingly, after one particularly nasty argument, Matthew put the phone down and refused to take any more of my calls. I didn't realise it at the time, but I would never speak to him again.

Shortly afterwards, I met Richard. It was a whirlwind romance, and within a year we were engaged and buying an idyllic farmhouse in the Norfolk countryside while I continued my journalistic career, commuting to London.

He was a successful singer and, as we toured the country, I thought I had finally found the excitement and love that I craved.

But Matthew was never far from my thoughts, and Richard complained that I often brought him into conversations, even comparing them both.

They were so different. Although outwardly romantic, Richard was repeatedly unfaithful, and I never felt secure enough to start a family with him. Eventually, after three-and-a-half years together, he walked out, having admitted his latest paramour was pregnant by him.

My life fell apart. Over the next year, I struggled to pull myself back together and did a lot of soul-searching. I finally understood what my father had meant. I realised Matthew was the only person who had loved and understood me.

When I heard through a mutual friend that he had split up with Sara, I wrote to him, apologising and asking for forgiveness - and a second chance. It was six years since we had last spoken, but naively I thought he would want to hear from me.

What I didn't know was that Sara was still living at the house and it was she who opened my very personal letter. It included my phone number, and she left me several angry, hurtful voicemails.

Yet again, I had inadvertently caused problems in Matthew's life, so it was unsurprising I never heard from him, despite writing several times over the next few months. In the end, I left it at birthday and Christmas cards, thinking he'd find a way to get in touch if he ever changed his mind.

Then, I heard a couple of years ago Matthew had married his new partner, Nicola. For a few moments I couldn't breathe, then the tears came.

Matthew and Nicola still live in Essex and, as far as I know, don't yet have children. That's the next milestone I truly dread.

It's been 11 years since Matthew and I last spoke, and I have to accept that door has closed.

Perhaps he has found what he is looking for and I am a distant memory.

I have had one other significant relationship since Richard - with Rob - but that recently ended after four years. Rob reminded me a lot of Matthew. He was decent and honourable, the life and soul of the party but with a kind and sensitive side.

But we were each too jaded by previous heartbreak to make it work. And while I wanted children, he had a grown-up son and didn't want to start over again.

So once again I am on my own, my mind full of 'if-onlys'. If only I'd stayed with Matthew, we'd almost certainly be married with children.

Or, maybe Matthew wasn't the right man. I will never know the answer, but my decision to leave him has definitely cost me the chance of ever becoming a mother.

Now I can only look back and admonish my selfish, younger self. When I visit friends and family back in our home town, I can't help but hope I'll bump into Matthew.

I'd like to think I'd say sorry. That I will always be there for him. But I wouldn't be surprised if he turned his back on me and kept walking.