Ray Kluun is a young Dutchman who slept around while his wife was at home dying from cancer. This might have remained a matter for him and his conscience if he had not then written a book about a young Dutchman who sleeps around while his wife is dying from cancer. In Kluun's case one of the partners became a serious and long-term lover. So too with the man in his book. We see him texting the girlfriend to fix the next date even as he is coming and going from his wife's deathbed. Kluun's more polite detractors have called him things like "heartless shit" and expressed regret that it was not he but his wife who died.

Even this might have remained a matter for Kluun, his conscience and his admittedly large circle of friends if the book had not then gone on to become a bestseller. Its English title is the provocatively ambiguous Love Life. In Holland alone it has shifted more than half a million copies in the four years since it was published and has been translated into dozens of languages. So the rage has spread, metastasised. But it is an anger that is tangled up with all sorts of other things, not all of them malignant. These include prurience, fashionability, curiosity and admiration. "Some have said I'm the biggest arsehole in the hemisphere," says the author, "and others have called me the new Messiah of Love." Whatever he is, his book has ignited a fierce debate about fidelity, sex, and the nature of unconditional love. It is as if a producer with a killer populist instinct had sampled the best grooves from John Gray's Men Are from MarsŠ and Erich Segal's Love Story, then fronted them with a highly assertive line of confessional rap.

This, for example, while his wife, already ill, is away for the weekend on an annual outing with colleagues:

"Three o'clock. When you're having an affair you learn how to value time. Especially at night. Normally at about this time you have to choose between going on drinking/dancing/chattering on and screwingŠ a bit later we're at her place putting my erection to all kinds of imaginative uses, and we keep it up through the small hoursŠ When I get home I ring Carmen [his wife]. I tell her I danced till four in the Hotel Arena. I don't mention the [Ecstasy] pill or Rose [his girlfriend]. Carmen hates drugs and Carmen hates infidelity."

Not as much as members of the Dutch literary establishment hate Ray Kluun. For them, however, his crime seems to be less one of licentiousness than temerity. For Kluun, 42, was an advertising executive, as is his book's narrator, Danny. Worse, he has brought all his old trade's opportunism to bear in marketing the work. There have been "guerrilla signing" sessions in the highbrow bookshops of Amsterdam, with Kluun fans turning up mob-handed, buying up all the stock of his book, while his publisher, the respected Joost Nijsen, merrily foots the bill and thanks the shop for selling so many copies. There was even a launch party in a set of rooms at the city's Arena Hotel converted into the main settings of the book's action. Guests were greeted by a "nurse" asking them to be silent because there were some very sick people about; a "psychotherapist", another character in the book, was available to them if the need arose. Right from the start, Kluun had networked among his old associates to fast-track the process of getting his manuscript read by a publisher's editor.

The object of all this controversy can be found in a big house in Johannes Verhulststraat, a well-to-do street in Amsterdam's Oud-Zuid district, not far from the great Concertgebouw. Invitations to go on identifying Kluun with his hero, or anti-hero, become increasingly hard to resist since this is the very street where he and his wife come to live towards the end of the book and the end of her life. The parallels continue. The room in which I eventually sit down to talk to Kluun is the one where his wife lay in her coffin, having died one floor up.

On the wall are photos of a younger Kluun with that wife in her voluptuous days. That was just after the breast cancer had been diagnosed, but nearly two years before the illness had ravaged her down to six stone and the brink of death and the doctor came with his euthanasia potion. With the couple in these photos is their daughter Eva, who was then three and is now nine. They all look in the very pink, with, what, 40 or 50 years together stretching out before them. The reality of course was that even as the shutter clicked, the cancer, undiagnosed six months previously, was already getting to work ­ and he had been sleeping with too many women to remember. Once his wife was ill, the number of other women reduced from dozens to a "handful"; Kluun did not make it his business to tell them about his wife at home. In this room too was the long farewell party that took up residence for a week or two in Mrs Kluun's final days.

So, to come here is to enter the rooms of the book. I was going to say "enter the novel", since that is how it is billed, yet by the end of the story there is so little difference between the death of the real Mrs Kluun and the notionally fictive one that it could hardly have been a truer account of a close death if it had styled itself memoir or documentary. Even Kluun's friends, relatives and colleagues are in it, albeit with altered names. One of them, a young woman who detected elements of herself, was so angry with him that she could not speak to him for six months.

Soon after I have entered the house a woman appears in the hall. It is so obviously the woman that he ­ and his counterpart ­ was having an affair with that there is no need to ask. This is the one who, towards the end of the wife's life, finds that she too can no longer conceal her own jealousy. She has since acquired that identity herself, having married him last year. They have a daughter of three who bears the name Rose, which is also the name of Danny's lover in the book. It is tempting to ask him about the morality of putting people into books and then playing the fiction card when challenged. We do come on to that, but for the moment it is properly upstaged by other questions. Like, do you still sleep around?

"Ah, this is the one that people always ask me," he replies, apparently as unflappable as someone who is always being asked this one. "Whenever I am doing a reading, I just have to wait for this question." And here it is again now. "I say, ŒAnd you?'" he replies. "Sometimes they say ŒI don't', or else they just laugh." I say, for what it's worth, that I got married last year, as he did, and that I didn't ­ don't ­ see sexual relations with other women as part of my future; putting the morality to one side just for a moment, it's erotic to go on choosing and being chosen by one other person to the exclusion of all others.

"Well, I have read many books on promiscuity," he continues. "In Holland one in three confesses that they have done something with someone else in the past three years. When Natalie [Rose in the book] married last year, we said we don't promise to be true. We do promise to try to love each other and make each other happy. Part of that is being true to a certain level of honesty. But true [ie, sexual fidelity] is not an aim, not a way to make each other happy."

So if someone said, "Kluun, it has been decreed that you must never again have extramarital sex." What would your response be?

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