In January 1997 I remember reading one of the best pieces of travel writing I have ever read about a romantic weekend in Bruges. It was written by Kathryn Flett, editor of the magazine section of the Observer. What made it so memorable was that along with the usual details of food and hotel accommodation came the knowledge that the author's husband had just told her he was leaving.

This very public coda to their marriage was written with wit and pain in equal measure - an early example of what would later become known as "confessional" journalism.

Over the next few months Flett's descent into depression, followed by her gradual emergence into the light of another relationship, was charted through a weekly column called Girl Overboard. Now comes the book - a timely antidote to those life's-a-drag-but-hey!-you'll-get-your-man-in-the-end Bridget Jones-style gambols across the heartscape of contemporary life. The Heart-Shaped Bullet is by no means Kathryn Flett's Observer column between covers.

"I knew that voice would be irritating over that length and it wouldn't be believable," she explains. "Also my experience changed over the process and that needed to be reflected." The brave-face flippancy of the early days has all but gone.

The story begins with the wedding, backtracks to when the couple first met, then dives headlong into the misery of a failing relationship that finally imploded just 17 months after vowing to have and to hold for ever.

For all her media savvy, Kathryn Flett had dreamt of her wedding since Barbie days, when the frock rather than the Ken played the co-starring role. In many respects her story of how Mr Right turned into Mr Wrong is almost banal, she admits. Five of the nine marriages her friend Fiona attended in 1995, she writes, ended in divorce.

"But the banality of it, the commonplaceness of it, shouldn't detract from the intense amount of pain that can come as a result of these experiences. And I do think we live in a culture where it isn't out there and dealt with, and a lot of criticism I have faced and will doubtless continue to face, is the we-don't-want-to-know-this-icky-stuff and why-do-you-have-to-be-so-out-there-with-it? But it's the same reason that we should talk about the pain of childbirth, because people should bloody know.

"One of the key bits of the book for me was when I wrote about how shortly after being married, when everyone is saying, `Oh you look so fantastic and you look so lovely', how you feel you have to go along with this newlywed charade, whereas inside you're saying `Why aren't I feeling as fantastic as the world is expecting me to feel?' "

The book's ending is unexpected - as much for the author as her readers. After surviving her marriage breakdown, Flett embarked on a new relationship. When this too came a cropper, she went crashing into a full-scale nervous breakdown ending up in a psychiatric hospital. The book at this stage was two-thirds complete, but the inclusion of this concluding episode meant that Flett's planned look at the state of contemporary marriage and relationships - her original ending for the book - was abandoned.

Flett's analysis-in-hindsight on her own marriage is that they should never have married. Yet there is no sense of victory. The girl sitting opposite me in the kitchen of the west London flat - bought in the full flood of romance, and where she now lives alone - is still very wounded.

"He very much presented himself as the person I wanted him to be. And when he changed so dramatically, really as soon as we were married, I felt very disarmed and I didn't know how to get back to what was there at the beginning.

"Maybe it should have been a great affair that lasted six months. I don't know. But it's difficult to have maybes about it, because we married and for me the fact of marrying did change the whole trajectory of the relationship."

Has her experience given Flett added insight into relationship meltdown? The disparity in their incomes and lifestyles played a part in her case, she believes. While he taught blind children, she was a high-flying media babe, one of a generation of young women unused to compromise.

"Because there's an awful lot at our fingertips. We have been able to do a lot more than anyone before, and it seems to bring with it a sense of self-entitlement, which is not necessarily a good thing. A feeling of my-life-should-go-like-this, I can control this, I can control that."

It's when this sense of self-entitlement extends to emotions rather than just a car or nice house, she says, things you can't control, that the difficulties begin.

"Like your relationship to a new-born baby - why don't I love this child as fiercely as everyone told me I was going to?" The feeling that "I have a right for everything to be perfect" isn't conducive, she believes, to sticking it out. It's a trait that until recently has been more prevalent in men. And Flett believes that her husband "very much bailed out". The business of "something brighter and shinier and newer and more distracting and that grass being greener and that `different' necessarily equates to `better' and that somebody else is going to plug in the gaps". He is now on wife number three.

As for the ethics of confessional journalism, Flett believes the only criterion is that "it is honest and it is well written and doesn't set out to hurt gratuitously". Did writing so publicly help her get through it?

"I don't know. I'll get back to you when I'm far enough away to see if catharsis takes place."

The Heart-Shaped Bullet will be published by Picador this Friday, price £9.99 in UK.