Sex sells, they say, and I’m as guilty as anyone of finding headlines such as “How to keep the sex alive in your marriage” irresistible. I pore over these articles, never quite trusting their advice, but still discussing them with my girlfriends ad infinitum.

But is sex really about love, about connecting with your partner in some mysterious, profound way?

No, I don’t think it is. I think the 20th century made the whole story up, and we bought it because it suited us. We went from sex-shame to sex-worship in a few heady years.

We are told again and again that sex is “communicative”. I always think, “What are they talking about?” Have I ever communicated anything during sex? I don’t think so. Some women are confident enough to tell their partners exactly what they want in bed, so yes (I mustn’t be totally cynical), you might just communicate as well as you do to a plumber, explaining where a leak is coming from. And just being naked with someone is a real act of trust. But beyond this, I have absolutely no idea what is going on in my partner’s head when we have sex, and he has absolutely no idea what is going on in mine.

I once risked asking my partner whether he thought sex could ever be spiritual. “Spiritual!” he laughed. “The spirit doesn’t enter into it. Sex is about lust, about desire, about a particular physical experience that is intensely pleasurable. It’s about Spurs coming top of the league, a good day at work, a way of dealing with surplus emotion which makes you able to sleep well. Sex has never been about the spirit, not for a day!”

One of the most alarming things about sex, I find, is the role of fantasy within it. Regardless of whether it is true, we are still taught that sex is about love. There seems to be a huge conflict here. Having sex with one man, thinking of another – am I persuaded that counts as “loving”?

In the early 80s, as part of my training as a probation officer, I learned how to be a sex therapist in a week. No mention of the word “love”, incidentally: it was all technique and teaching my “clients” how to fantasise about film stars.

At that time, I thought it was all quite amusing. I was in my 20s, and quite happy to share erotic stories with my then husband, about innocent virgins and their seduction. But now I am 56: and thank God I don’t know what goes on in my husband’s head.

We were lovers, first, at 20. Is he remembering how smooth and silky and firm my flesh was then, as he feels my middle-aged spread? Is he thinking of the lovely young woman who’s just started at his work, the one who is “turning everyone’s head”? Or is he just away with the fairies? I once asked him what it felt like as a man to have sex – and he told me he felt like a bicycle tyre being blown up. Oddly, I found this hugely reassuring. It could have been so much worse.

And what if he could see what was in my head? What if he knew I was thinking of a scene from a Japanese pornographic movie I saw yonks ago? I complain that sex is not communicative except in the most mundane ways. But what if it really was? What if, at the end of the sex act, we swapped printouts of what we were honestly thinking about, whether that consisted of shopping lists or secret objects of lust? Would we feel closer, more loved by our partners? Or would we feel undermined, betrayed, jealous, appalled?

Sex is not about souls. We have sexual desire when we want to have sex, not when we love someone. If that wasn’t the case, it would be the oldies who were all having rampant sex after 40 years of a happy marriage, who’d be the writers of agony columns advising those poor young people how being kind and considerate and bringing a cup of tea to their partner in bed will really get the pulse racing.

The older I get, the more sceptical I get. Sex is a neutral and colourless thing, and a higher or lower sex drive is caused by hormones that are hard to control. For hundreds of years, societies and religions have tried to harness this drive. But for the past 60 years, we in the west have been quite sure we know best: every other age and culture has been wrong. We are right. Sex is the most profound form of human love, the deepest expression. What a load of nonsense. How were we ever taken in? Because we wanted permission to have a good time.

Sex is not about souls, it’s about bodies, and the thing about bodies is that they are objects: don’t complain about men treating them as such, we women treat them like objects, too. We pierce them, tattoo them, adorn them, beautify them to our heart’s content. I was bemoaning this fact to a gay friend of mine, saying: “It’s dreadful and destructive what modern culture would have us believe. By conflating sex and love, we have young people wanting plastic surgery to change their bodies. They think that by having surgery they’ll become more shaggable, and therefore more lovable. Isn’t that pathetic?”

Nowadays, for people who have been married for a long time, sex is the minefield that separates them

He said to me: “Of course sex is about bodies. And what are the young people who don’t want surgery so complacent about? We have the technology. They should be having surgery, too.”

I am such a romantic. I believe in love from the bottom of my heart. There’s a couple in our village who have been married for 60 years: I watch them walking their dog every morning, hand in hand. Where has that kind of love gone to? Will we ever get back there again?

Nowadays, for people who have been married for a long time, sex is the minefield that separates them. Everyone feels they ought to be having it, ought to be enjoying it, that it ought to be an expression of their love. They are too tired for groundbreaking sex, but they hunger for affection. Human beings crave to hold and be held, but we stay on our side of the bed in case a sexual performance is demanded. It’s all a very sad and sorry story.

How did we get here? Where did we go wrong? Why are so many relationships just so fragile?

Love and erotic love are two very different emotions – I would argue they are almost contrary. Love proper is to do with the other person: it is about the care, respect and understanding of that human other. Love like this grows, it cannot help it. The more of yourself you invest in another person, the more you receive. You become as one: their pain is your pain, their joy, yours too.

Erotic love, on the other hand, is about wanting something.

The French are right: you cannot desire what you already have. In fact, another article I recently devoured was written by a French sex therapist. It was about how to have a fulfilling sex life in your 60s. I wanted to disparage it, as I do all the others, but she was absolutely right: keep yourself in trim, buy sex toys, watch pornography, have an affair if you dare, keep yourself aloof from your husband, sleep in a separate bed, use a separate bathroom. And certainly don’t allow your husband into your innermost thoughts.

I put the paper down and I thought, “That’s all very well, and true, but who would want a marriage like that?”

Marriages all about me fail: every time, it’s unbearable to me, the children are always distraught – as mine were when I divorced – and sex, in one guise or another, is always the reason. Either one of the partners has “fallen in love” with someone else (ie, fancies someone rotten and wants to pursue it), or there is simply a mismatch (and perhaps only temporary) of libido. I just don’t buy the “deep incompatibility” malarkey – love and sex being bedfellows, the one reflecting the other. It’s far more likely you’re working too hard or have got young children.

If you want a good marriage, forget the hysteria about sex. Just take care of your partner, have a good chat, make sure they’re OK, and give them a good, felt, daily hug.

Possibly a Love Story by Olivia Fane is published by Arcadia, £8.99. To order a copy for £7.64, go to bookshop.theguardian.com or call the Guardian Bookshop on 0330 333 6846