Dear Uma, I'm your number one fan...

Stop All the clocks. National heart-throb in breeches, Colin Firth, this week committed the ultimate act of betrayal - and, cruelly, just before the repeats of Pride and Prejudice, too. He and his stunning, thin, Italian bride, Livia Giuggioli, reportedly wept during the ceremony, but he should know that the rest of us will be weeping for a good deal longer.

Lust object of the fortnight, Tim Henman is equally casual to the plight of his female fans. Apparently, Henman thinks it rather sad and strange that women spend hours in the rain waiting for a meaningless encounter. Which is rather strange of him. For we never grow out of crushes. The organiser of the Henman fan club is, after all, not some besotted teenager, but a 25-year-old who considers it a very worthwhile use of her time.

The increasing value ascribed to celebrities means that what used to be considered childish now gets called normal. Staying in to watch ER because of a George Clooney obsession? Fine. Grown men arguing for their favourite Spice Girl? No really, it's healthy. Henman's bleak request that such admirers should "get a life" will be over-ridden by our unabating ardour. Most desperate of all, some fans are even fulfilling their desires. Gary Numan now lives with one-time fan 29-year-old Gemma O'Neill. Adam Ant's girlfriend adored him from afar from the age of eight. Even the mighty Anthea Turner had a teenage crush on Peter Powell, then a Radio 1 DJ, before she became famous herself and nabbed Powell for her husband. And Minnie Sharp, wife of Beverly Hills 90210 star Luke Perry, was named the patron of the obsessive fan when she won her man by sending him one of her bras through the post.

Being a lustful fan of someone is part of the group-bonding process these days. It creates instant rapport between people. Thirtysomethings who used to swap Dr Who stories at school now likely to engage in heated discussions about whether ER's Dr Ross is a hopeless womaniser or a miraculously reformed character whose heart truly belongs to Nurse Hathaway. "It can be a healthy part of a fantasy life. People are more open to it now, celebrity is a more normal part of everyone's experience," says Julia Cole, psychosexual counsellor and spokesperson for Relate. "It's only unwholesome when it becomes too obsessive," says Roger Look, clinical psychologist for Solihull Health Care Trust, "when it prevents the individual from forming healthy, normal relationships, when it is still all-consuming at 40, or when it leaves the other partner in a relationship feeling inadequate or jealous because, as a real person, they can't possibly compete with the perfect fantasy."

Cole says that the trouble with pursuing a celebrity is that you cannot possibly know them. Elizabeth, 35, a programmer, in love with Colin Firth, says that you can know a celebrity as well as any other object of lust. "You don't know someone who you meet at a party until you get to know them. It's all about intuition. I know as much about Colin Firth as I did my last boyfriend when I started going out with him. Relationships always start on hope-for-the-best policy." In a world of Internet relationships and blind dating via the lonely-hearts columns, is fancying a celebrity any more unrealistic? Elizabeth is phlegmatic about Colin Firth's betrayal. "I find my crushes fizzle out after a while. It'll be rekindled when Pride And Prejudice gets repeated, but I'll soon be on to some one else. I got over Matt Le Blanc, after all."

The joy of the celebrity crush is that it allows one to experience the thrill of new love without having to be unfaithful. It doesn't matter that it will never happen. "Some people pretend that their partner is the celebrity some of the time," says Cole, "but nobody has to know. It can be a good outlet."

The reality that you can't move for celebrities in our star-obsessed culture means that more people have access to them and more people end up with the stars who were once just posters on the wall. Cole worries that these relationships, hinged on one-sided adoration, might be unbalanced. "While all relationships are about shifting control, this one will inevitably involve the adoring fan coming down to earth pretty quickly," she says.

But from the celebrity's point of view, the imbalance is perfect for their fragile confidence. Music PR and events organiser Anita Strymowicz says that the attraction is good for both sides. "Pop stars are pretty lonely people. It's a bit pathetic. But most are neurotic headcases and if they can find someone who adores them and who will always say how wonderful they are, they will." While Strymowicz has spent much of her career surrounded by screaming 14-year-olds, she agrees that celebrity crushes can now be a lifelong commitment. "I know a lot of music journalists are still pining over Jason Orange, well into their thirties."

And while it is traditional to pity the lonely fan, in fact, celebrities can come off worst. For a fan can always enjoy their fantasy from a distance, but a celebrity has to walk around in the knowledge that, in the flesh, they are going to disappoint people for the rest of their lives.

"My friend met David Sylvian," says Strymowicz, "she had loved him for years. It was at a party. Then she heard the toilet flushing and she saw him walking out. She hadn't thought of Sylvian performing bodily functions. That and the discovery that he wasn't short sighted but the glasses were to make him look more intellectual put her right off."

"I classically confuse the celebrity with the part they're playing," says Amanda, 29, a TV assistant producer. "You think they're going to be wonderfully sexy and intelligent and they turn out to be over-pampered and not interesting at all. I remember James Spader saying that he always gets cast as bad cops or brooding sexual misfits when actually he is married with three kids and lives in a normal house in Boston. The truth is that people with those kind of 'fascinating' personalities really are bad cops or sexual misfits, not actors. If an actor were that weird he'd never get any work." Amanda's former partner was an actor who was just beginning to get adoring fan mail after appearing in a BBC costume drama. "He thought it was great. I found it very odd being on the other side of it all."

Men and women's celebrity crushes are very different in nature. Women think that they know the celebrity, that they can read his misunderstood soul like nobody else. Men are more down to earth. Pamela Anderson's many college-educated male fans are rarely in love with her personality. "I fancy celebrities who look like they would be demons in the sack," admits John, 32, a political journalist. "Kate Moss and Sporty Spice look really dirty. Then, there are fit women who look like they might be quite clever, likeUma Thurman."

It is rare to hear of a male fan ending up with a female star. Maybe women stars are more suspicious of blind adoration. While a woman sending a bra though the post is at worst a waste of good underwear, when a man does it, it can be sinister. "I told one celebrity's publicist that I had always fancied the celebrity I was going to interview," says John, "By the time it came to our interview this had been blown up out of all proportion. The celebrity in question was clearly terrified."

Best of all, the celebrity crush allows one to enjoy completely inappropriate love affairs from the safety of the armchair. Nobody gets hurt, and as soon as some one better comes along, you can dump them.

How do we love them?

Relationships with celebrities - real or imagined - come in many guises. The key is to identify your needs

LOVE THEM, HAVE NABBED THEM

The hip option for a member of the public and increasingly popular in the confused, post- modern world, where celebs are a dime a dozen. Make a heart-throb a notch on your bed post before they make you one on theirs.

LOVE THEM, WANT TO MEET THEM

Go ahead, join that premiere throng, bribe that doorman, sneak into that hotel laundry basket. You know you belong together. But remember, there's no better way to cure yourself of the problem than to find out how boring you heart-throb really is.

LOVE THEM, DON'T WANT TO MEET THEM

The well-adjusted victim enjoys the thrill of watching Colin Firth's every twitch while fully aware that actually meeting him would reveal just how, strong and moody he isn't really.

Subdivided into:

Character: In love with Mr D'Arcy as played by Colin Firth.

Actor: Love for Colin Firth himself has endured at least three costume changes.

FANS WHO LOVE TOO MUCH

If you cry when they get married, form a fan club or have told your partner that "George Clooney wouldn't treat me like this", it's time to pull yourself together.