David, my boyfriend, as I still like to describe him despite his being 77 and me 67, was lying in the recovery ward of the Royal Marsden Hospital when he proposed to me. It was only a couple of hours after his major surgery for liver cancer and he was, amazingly, sitting up in bed with a cup of tea, wired up to fentanyl, dripping pain-free elation. I was thrilled to see him in such good condition.

‘Will you marry me?’, he asked in a slightly slurred voice.

It took me only a heartbeat to answer ‘no’.

That morning we had travelled down in a lift to the operating area of the hospital and I had kissed him goodbye. I wasn’t sure I was going to see him alive again. A nurse saw me looking tearful as I began my journey back upstairs and said cheerfully: ‘Don’t worry, he’ll be OK. What cancer does he have?’ When I answered liver, she didn’t look so certain.

It’s now three years on from that sickbed proposal, and 20 years from the start of our romantic relationship, and he’s still here and we’re still not married.

We met in 1976 when Jane, my best friend then and still now, suggested I join her and a nice man she had met at a party. They were to meet outside Browns on South Molton Street which was having a sale.

Browns was then the most fashionable boutique in London and, aged 19, she and I had just left school so that was not our usual stomping ground, but David was ten years older, so I assumed this was the kind of thing glamorous older men did.

As it happens, David, who was then a researcher at Granada TV, was there waiting on the pavement but no Jane. He was skinny, good-looking, with thick, curly hair and a warm and friendly Puckish quality.

David and Alexandra met in 1976 after being introduced through friends

We were always pleased to see each other across the room at a party, and sometimes he would accompany me at events I went to as editor of Vogue

I don’t remember whether we went into the shop, especially because as I now know, David doesn’t buy clothes from expensive boutiques, but we had a burger together across the road in The Widow Applebaum’s, then a well-known deli.

We’ve remained friends ever since – through the birth of his two children with his long-term girlfriend, and through my 20s and 30s, my marriage and the birth of my son, Sam.

We were together on group holidays with friends, including one with David and his children once he had separated from their mother, and Paul, then my future husband, and his children.

On countless occasions David and I were the spare singles at a dinner table. We were always pleased to see each other across the room at a party, and sometimes he would accompany me at events I went to as editor of Vogue. He was an excellent plus one with his gregarious nature and curiosity about everyone and everything.

When, in 2004, both his mother and my father died, we were confidantes in grief.

A few months later, I rented a house for the August bank holiday to take my newly-widowed mother out of London. My son Sam was nine, and I invited a couple of close friends with their two children to join us.

Since my mother is not exactly a down-on-the-knees-with-the-finger-paints type of grandmother, I wanted to include someone to amuse her when we were immersed in childcare. Enter David, whom I collected from the train station wearing a particularly unattractive beige mac. There was no thought of romance from me.

It’s true that over the years, many of our mutual friends had suggested we might get together and, now and again, I thought it would be the perfect answer if we could. But that was immediately followed by thinking we couldn’t. The magic just wasn’t there, and what a risk to a wonderful friendship if it all went wrong.

It was in a lush Devon valley, he in his 50s, me in my 40s, that our romance began

David, though – I don’t think he minds my saying – had nurtured a tendresse for me for some time, although I might add that did not make me a member of a particularly small club. He was known for his astonishing number of short-term liaisons.

But it was on that August bank holiday, nestled in a lush Devon valley, he in his 50s, me in my 40s, that our romance began.

It took me completely by surprise. Jamelia’s Superstar was a hit at the time and I drove around the high-hedged narrow lanes singing ‘you must be some kind of superstar’ to myself joyfully.

I do remember thinking, as we lay together that weekend, that for some inexplicable reason I knew this relationship was going to work. Even though for months afterwards I kept holding my breath wondering if I was going to wake up and realise that it wasn’t. That we weren’t ever going to be more than friends. We were fooling ourselves.

Several people observed that I ‘did pick them’ with reference to David’s track record and my previous tricky amours. But Jane, slightly concerned at first about his staying power, felt all would be well having observed him looking at me with ‘cow-eyed devotion’.

David has never been married. It was one of the achievements he prided himself on, along with never going to Harrods. But I have – to Paul, who was my boyfriend in a tempestuous on-off way for about four years. During one of our splits, Paul arrived at our flat and confronted me with a date booked a few days later at Chelsea Register office and a ring.

I was 36 and realised we couldn’t go on like this, breaking up and making up. If I said no that would be the final end. It was a now or never moment and I said ‘yes’.

We married with only my sister and brother-in-law as witnesses. I bought a white dress from Ghost and – as it happens coincidentally – an embroidered white Dries van Noten shawl from Browns boutique and took the wedding day off from Vogue without telling anyone what was happening. It felt lovely marrying Paul. It was as if we had reached a peaceful conclusion. We were going to be happy with each other. Within weeks I was pregnant.

Six years after divorcing my husband we became a couple

I had never been particularly interested in being married, but having wed relatively late (most of my friends already had families), I had every intention of it lasting for life. Marriage brings with it a sense of stability and I was thrilled to be able to stop wondering whether I would ever marry, and to be in the next stage of a commitment to someone else.

But it didn’t work out that way, and the grim reality of living with someone as the marriage splinters and then cracks wide open is utterly miserable.

Four years later, Paul moved out.

I was in a hotel room in Berlin, staying there for a Vogue conference, when he told me on the phone that he wasn’t able to be the person I was asking him to be and he was leaving the house we shared in Queen’s Park, west London.

It was the spring of 1999. I looked out from my windows high above the desolate German city being rebuilt by hundreds of waving cranes and tried to pull myself together for the gathering of editors and publishers. I managed to get through the days, but, at night, I panicked about what my life would now become. And how my son would survive the split.

When I got home it was Sam’s third birthday party, a pirate theme. Both Paul and I were there, trying to put on a united front to Sam and the other parents, but after tea, Paul left with all the other adults.

I felt very alone – I was in my 40s and embarking on a new life as a single mother with a very demanding job – but I also felt relieved. Living with a husband in a precarious and combustible relationship proved to be way more stressful than being alone. I yanked down the voile curtains I’d always hated in the bedroom, got all the windows cleaned and suddenly everything looked much brighter, both literally and metaphorically.

It was six years after that painful separation before David and I became a couple.

By then, I had become used to being single again, though I wasn’t alone – I had Sam. My constant companion.

I had no desire to find a husband, but I did want to have someone else permanent in my life, albeit someone who could fit in with me and Sam.

Fortunately, David immediately did, never trying to take on the role of father, but always being there for Sam, quietly watching from the sidelines.

So why on earth did I say no when David so sweetly asked me from his sickbed to marry him?

To some, my reaction might seem callous and unloving – but I knew he was high on the painkillers, which struck me as an inopportune moment for a big declaration on which to base the rest of our lives. More importantly, the way we co-exist works and I am fearful of jinxing it.

When I refused his proposal, David didn’t seem remotely concerned. I asked him how he felt about it for this article and he said, no doubt partially joking, that he was probably relieved.

But possibly the point for both of us is that he said it. We didn’t need to go through with it.

Even now, we occasionally banter about the idea of getting married but never with any real intent. We live together, but David keeps his own flat and I own my house. We have separate finances and don’t even have a joint household budget.

But in many ways our lives are similar to married couples.

David makes the bed and the salad dressing; I do all the cooking and change the light bulbs. We do our own personal bureaucracy – bills, insurance etc, but we jointly organise holidays and our social lives.

It works pretty well most of the time, though not when one or other of us is driving, in which case, if we were married we would probably be divorced by now.

If David wants to leave me, there is nothing to keep him here, and similarly if I want him to go, it would be relatively simple in logistical terms.

There’s something very liberating about that. It means that the only reason we are together is because we want to be, not because there are any obligations to do so.

Perhaps my previous experience of marriage also underpins my attitude. I had the certificate and the wedding ring and that counted for nothing in the end, so it’s hard to see what the point is now.

Despite the number of divorces, marriage is a surprisingly enduring concept, and I have huge admiration for people who make it work. If you have children together, there is certainly something reassuring for them about the idea of that formal commitment. But we haven’t had any together and, although we are fond of each other’s children, we don’t feel responsible for them.

Last year, having had a health scare myself when I had a tumour removed from my colon, I did wonder whether it would be a sensible decision to marry. No husband could have been more supportive than David, who was loving, robust and practical throughout.

A confrontation with mortality does make you wonder about putting your financial affairs in order, and marriage can mitigate inheritance tax, which is why many long-term unmarried couples do eventually make their vows.

Whenever I see my financial adviser he has a go at suggesting we should tie the knot for the sake of Sam, who would end up better off if I die.

David could inherit my estate tax-free and immediately pass it over to my son without incurring tax. But only if David lived for a further seven years, which with our ten-year age difference is not a given.

Marrying for that reason strikes me not only as unromantic and not remotely in the spirit of how we love each other, but also tempting fate.

Since that proposal three years ago, from time to time I have thought how lovely it would be to have a wedding party with all our friends and family there wishing us well. Note that I say party rather than simply wedding. It would be the fun of the occasion that would be the driver. (I’m not marrying in secret again.)

But immediately that fantasy is followed by imagining the horror of organising it. We find planning anything together immensely difficult, so the idea that we could peacefully manage a big do is almost impossible.

No, it’s better to stay blissfully single, together in all but married name.