On Tuesday, February 13, Robbie Williams admitted himself to a rehab unit in Tucson, Arizona. A two-sentence press release issued by his patient press aide, Bryony Watts, made it clear that the matter was not open to further discussion with the artist’s people. “Robbie Williams has today been admitted into a treatment centre in America for his dependency on prescription drugs. There will be no further comment on this matter.” Camp Williams was keeping a dignified silence, even if the country wasn’t finding it easy to follow suit. The next day, The Sun ran a headline listing the extent of Robbie’s woes: “Happy pills, sleeping pills, 36 espressos, 60 Silk Cut, 20 Red Bulls every day.”

The highest highs and lowest lows of Williams’s career have become a modern fascination. And if he chooses to mark the uppermost peaks — such as signing an £80m contract with EMI records — with a characteristic remark such as “I am now rich beyond my wildest dreams”, then he should hardly be surprised if those ultimately footing the bill for those wild dreams are also interested in his troughs.

In 1995, after leaving Take That, he jumped onto a stage with his heroes, Oasis, with an abandon bordering on lunacy, high on anything he could get his hands on. In one pop of a flashbulb, Robbie Williams was transformed into the public symbol of that raucous, ungainly journey from boy to man. As with George Michael before him, the astonishing solo success that followed that one giant leap into the unknown would come to epitomise the idea of pop escape.

Williams’s musical career has been littered with plaudits. Over the course of a decade, he has been responsible for at least one modern pop classic, Angels, a succession of multimillion-selling, increasingly confessional albums, that record-breaking record deal and high-octane live performances that have wowed audiences from Brazil to Bangkok. He has also made a careful record of his ability to sex his way around the world, with few or no strings attached. At 33, he should be buoyed by a vigorous sense of self-improvement, shouting out loud and clear to working-class northern lads with little sense of entitlement but a bucketload of ambition that anything is possible. He should be the man to be. So why does his story seem so unappealing? Why does Robbie — now washed up on prescription meds, allegedly fearing that he is heading the same way as, at best, fat Elvis or, at worst, Anna Nicole Smith — seem so desperately unhappy?

The date of his entry into rehab could not have been more poignant. Not only was it his 33rd birthday, it was also the day before both St Valentine’s Day and the Brit Awards, the British record industry’s annual bun fight over who is biggest and best. Both would have been far from cheery occasions for him, if he were not in an exclusion zone in Tucson. In an unremarkable year for male solo artistry in British music, neither Robbie nor his latest album was even nominated. Entitled Rudebox, that album arrived with a bold proclamation by Williams that it was the record he had been waiting his whole life to make, but it has been a commercial lead balloon. Most notable, and most hurtful for Robbie, his old band, Take That, had the biggest-selling album of the season with their reunion package, Beautiful World. Watching them scoop the gong for best single at the Brits would have been unbearable.

Anyone who has met Williams will tell you the same thing about him: that he views the world as a series of little grudge matches. Part of his neurosis — and his incredible drive and ambition — is his inability to let things go. He still carries a burning and very public resentment towards Take That’s former manager, Nigel Martin-Smith. And on the song Good Doctor, he spells out the change he has made in his past six years of recreational sobriety, while living in LA: “The glory days are gone, and we’ve all stopped ’avin’ it. No raves no more, just bedside cabinet.” This is not a life that kids would aspire to. It is the antithesis of the modern dream of fame.

A little clue to the further sting of St Valentine’s Day can be found in Williams’s autobiography, Feel. Much of the narrative is taken up by his supposed search for a wife. Yet within it, there is little in the way of romantic acumen. There are tabloid stings set up with Rod Stewart’s former wife, Rachel Hunter. There are a couple of tawdry episodes with Westlife groupies and a hint that he may have had sex on a video shoot. There is his compulsive inability to sleep alone, which sometimes leads him to ask male friends to share his bed. And the whole thing is underpinned by an absolute absence of any form of intimate love in his life.

Which is, after all, why we have all fallen in love with Robbie Williams. He has come to represent the modern mess of celebrity, its damage and pitfalls. He was the last pop star to emerge before the reality-TV generation. He predates the inexorable rise of the gossip glossies. His lack of luck in finding personal happiness has gone hand in hand with his putting his innermost life on a public stage. In the upper echelons of celebrity, Williams is one of the few to have worn his heart on his sleeve. We know far more about him than we do about his only peers in the top tier of young British celebrity: the Beckhams and Kate Moss.

When I last interviewed Williams, I asked him how long he had been single. He said five years. I commented at the time that after a spell like that, a woman of similar age might be sent into a panic, thinking that she was unmarriageable, that she might not have children. He said, with rather doleful eyes: “Yes, I suppose she might.” I then asked him when he had last been in love. There was a sharp intake of breath, and he whispered: “Never.”

Since he went back into rehab, it has been clear that Robbie Williams is still the nation’s pet project, perhaps more so than ever. Every woman wants to save him, see?

Explore Celebrity

• People

Times recommends

• Live chat: Thrifty ways to update your winter wardrobe
• Is anybody out there really listening?
• Nutrition Q&A: Will eating late make me fat?