Within a few weeks of falling in love, 29-year-old Gracie was virtually living with her boyfriend in his beachside flat and sharing his personal computer. These days sharing a computer with a lover can be more toxic than sharing a toothbrush. And so it turned out for Gracie.

Like all the women interviewed for this article, Gracie, a human resource manager, insists she is no prude. She is a willing sexual explorer. But even she was surprised at what her 33-year-old boyfriend, a builder, stored under his "favourites" file. "There must have been 20 porn sites there. I was pretty shocked - not that they were there - only that there were so many," she says. "Whenever I put anything into the search field, there would generally be a site related to porn come up. So if I typed in a word starting with 'L', I would get a listing of 'Lolitas', 'lesbians on lesbians'. . . You get the picture."

His internet history file unleashed a tsunami of pornography. But what is a girl to do when she is madly in love, is not averse to a bit of pornography and considers herself to be "cool"?

She tiptoes around the subject for weeks. She raises the issue gingerly: "I'm totally fine, just wondering why there's so much."

The internet has brought an explosion of pornography into the home and workplace of Australians. And the kind of material available exceeds imagination. The impact of internet pornography on sexual attitudes, practice and relationships may prove to be as profound as the introduction of the contraceptive pill in 1961. That momentous event helped usher in the sexual revolution, bringing the potential for worry-free sex first to married couples, then to singles.

The rising tide of internet pornography is giving some Australians the best sex education of their lives. It has the potential to extend sexual repertoires, re-invigorate flagging sex lives, increase tolerance and assuage hang-ups. It opens new horizons for the sexually curious. People can explore every possible sexual niche.

But internet pornography is also turning out to be the new marriage-wrecker, according to counsellors and psychologists. It is having a profound effect on relationships. More and more clients cite internet pornography as a factor in their relationship breakdown.

The technology has created an affliction that some call addiction, and others, more cautiously, call a compulsion. Internet pornography is a new outlet for those with pre-existing compulsive personalities, and it makes it easier for others, as a former head of the US Matrimonial Lawyers' Association, J. Lindsey Short, said, "to engage in the sort of behaviours that traditionally lead to divorce".

Whatever the label, increasing numbers of men appear to be hooked on internet pornography, and the women in their lives are flailing about in unhappiness, self-doubt and self-blame.

Michael Flood, a research fellow in gender studies at La Trobe University and co-author of the 2003 report Youth and Pornography in Australia, said: "This is not about couples going to the porn store to spice up their sex lives. Men in growing numbers are using porn in ways that are secret, shameful, and damaging. It is having a damaging impact on intimacy and sexuality."

It is difficult to determine the scale of the problem. A survey of more than 9000 American internet users by Alvin Cooper and colleagues in 2000 concluded that about 9 per cent were addicted, spending more than 11 hours a week looking at porn. A 1998 survey of internet users by David Greenfield, founder of the Centre for Internet Studies, found almost 6 per cent met the criteria for compulsive use, with porn sites and chat rooms most seductive. The godfather of US sex addiction research, Patrick Carnes, author of In the Shadow of the Net: Breaking Free of Compulsive Online Sexual Behaviour, claims 3 to 6 per cent of people are sex addicts. An Australian survey of about 1000 porn consumers by Alan McKee and colleagues found 0.4 per cent said they had an addiction. But online surveys are flawed: they are not based on representative population samples, depend on self-selected participants and lack control groups.

What seems undeniable is that a subset of people spends so much time porn gazing online that they are damaging their relationships. The Age has waded into uncharted waters to chronicle the impact of the compulsive use of internet pornography on relationships. Psychologists, relationship counsellors and men were interviewed.

But it was the long and candid interviews with women aged 25 to 50 whose partners were obsessed with pornography that was most illuminating. The problems may be confined to a minority, but it was surprisingly easy to find women whose lives had been turned upside down by their partner's online activities.

The same themes emerged repeatedly. The men spent hours online, searching for progressively harder core images. Family time or couple time was the first casualty. Sex lives floundered and withered away as men lost interest. Men became, in the words of Dr Margaret Redelman, president of the Australian Society of Sex Educators and Researchers, "lazy lovers". In the end they could not be bothered with real-life sex. In other cases, sex lives became porn-like, male-focused, extreme and lacking in intimacy.

Women's self-esteem nose-dived. They felt they could not compete with the nymphs on screen. They did not measure up to the bodies or sexual performance of the women their men were watching. Connie, a 50-year-old graphic designer, whose former partner looked at pornography constantly, says, "After a while I started to feel worthless." Karen, 44, whose eight-year marriage broke up over her husband's porn obsession, agonised over "why he preferred that to me".

A well-conducted British survey based on a representative sample of partners of regular porn users shows these feelings are widespread. While most partners are largely neutral about their men's regular pornography use, the survey, published in the Journal of Sex and Marital Therapy in 2003, shows that about one-third of the women found it highly distressing. About 32 per cent said their partner's porn use had adversely affected their sex life, 39 per cent said it had negatively affected their relationship, 34 per cent their self-esteem, 41 per cent felt less attractive and desirable since having discovered their partner's use, and 42 per cent said it made them feel insecure. More than one-quarter viewed it as a kind of affair.

The Australian women interviewed felt betrayed and inadequate. And always they were under pressure not to appear controlling, uptight or unreasonable. Men's consumption of pornography is natural, many believe, and to judge it as anything but positive is to risk being labelled a prude or, worse, a nag.

"I really thought I loved him and I did not want this to ruin our relationship so I always trod very carefully," Gracie says.

Her boyfriend's pornography consumption affected their sex lives, and then their relationship. The sex became impersonal and aggressive: "It became more 'porn' style - pulling my hair, no kissing, slapping around a bit, all stuff I was initially OK with," Gracie says. "There was no real intimacy, no thought about what I might like. That's when I began to realise . . . "

Slowly the sex started to taper off altogether as the internet porn began to consume her boyfriend. "I would wake up and find him looking at it, I would go to bed at night and he would look at porn," Gracie says. "We would argue, he would look at porn. I would take the dog for a walk, and he would look at it. I would brush my teeth, he would use it."

She blamed herself. He blamed her. She questioned, she cried, and finally, after a violent argument, she left.

A team of American researchers from Stanford and Duquesne universitieshas called cyber-sex compulsion a "hidden public health hazard". Sex counsellors and psychologists in Australia are less colourful. Brett McCann, a senior lecturer in the sexual health program at the University of Sydney, says it is a growing problem "with big implications for the public health dollar. There's no quick fix, and by the time the problem is uncovered, there's usually a crisis in the relationship."

Greta Goldberg, a clinical psychologist for more than 30 years, has counselled adolescents aged 13 and 16 for internet pornography addictions, as well as adults. "It's more pervasive, it's catching more people, and it's likely to be a huge problem in future," she says.

Relationships Australia, the country's biggest counselling network, reports an increased number of clients raising the issue. Pamela Lewis, director of client services, says, "More women are saying, 'We used to be close, now he spends his time on porn sites.' It's another one of those things wrecking relationships."

Dr Amelia Haines, a therapist at the Sydney Centre for Sexual and Relationship Therapy, reports seeing a lot of people for whom internet pornography is "out of hand".

"Men want to see what else is out there. Some end up spending three hours a night looking for the right image, the right trigger. They search and search. Usually what they look at is not too scary. They worry more about wasting so much of their lives; they're embarrassed about how much they're accessing, and they can't stop."

Compared with alcohol problems, and violence/control issues in relationships, obsessive pornography use is still a second-order marriage-wrecker. Usually it is part of a constellation of problems.

Ironically, the lack of high-speed broadband in Australia has kept internet porn's full potential on a leash. Slow downloading has helped maintain the popularity of old-fashioned video pornography. Even so, figures from Nielsen/NetRatings NetView show 2.7 million Australians visit an "adult" website in a month. (This figure counts repeat visitors to adult websites only once); 4.3 million clicked on at least once in a three-month period. More than 35 per cent of all people who used the internet in the quarter ending March 2007 visited an adult website at least once.

For couples in trouble over internet porn, it is a secret misery. Women said over and over the problem needed to be brought out in the open. "I'm glad you're writing about this," they said.

Rebecca, a 25-year-old medical student, strives for a clinical detachment from her fiance's obsession with pornography. She thinks of his problem as an addiction, like other substance abuses, characterised by compulsive use, secrecy and shame. "It should be treated like any other addiction," she says. "And abstinence is the best course." She says his problem is tied to low self-esteem, even though to the world, he appears a "charismatic, outgoing person". With porn, he did not have to worry what others thought of his performance.

But during the three years of "struggle" over his obsession, she has not always been so objective. "I was always the one pushing for sex," she says. "If anything, I'm more of a sexual deviant in bed."

Originally he confined his daily porn gazing to when she was not in the house. A quick flick through his internet history revealed an escalating habit. It reached a point where "porn became easier than actually having sex", she says.

She felt about as sexy as a "can of kidney beans. I felt unwanted. I found myself going to the internet and asking what is it those women have I don't. I felt worse about myself. I told him, 'I'll give you whatever you want. What can I do to make it more like porn?' "

Ordinary women's desire or desperation to "make it more like porn" has helped fire the popularity of the Brazilian wax industry, according to Nancy Etcoff, a Harvard Medical School psychologist, and author of Survival of the Prettiest: The Science of Beauty. Unlike the natural-looking porn stars of the 1970s such as Linda Lovelace of Deep Throat fame, the nymphs populating internet porn today have their pubic hair ripped out by the root after an application of hot wax. The desired look is "clean" and pre-pubescent. "Women today are emulating porn stars who have no pubic hair," says Etcoff, "and I think men like it."

Many women like the look, too, but a disgruntled Brazilian wax sufferer opined on a website: "Because girls are always so keen to be every man's fantasy, we did it, and now it is considered the norm to go through the extremely painful and costly experience of having all our pubic hairs ripped out every three weeks. My older sister never had to go through all of this."

The secret use of pornography is the true home-wrecker, according to most of the psychologists contacted. The most common pattern is for one partner to eventually discover the other's obsessive use. "When it's consensual use in a limited way, it's unproblematic," says Eric Hudson, national president of the Australian Association of Relationship Counsellors. "But where it is secretive, it is experienced as a betrayal of the relationship."

And secret use, he says, like an affair, can be a symptom of other problems.

Alex, a 38-year-old computer programmer who worked at home, describes himself as an "ex porn junkie." He admits the deception over his porn use was the last straw in a faltering 12-year relationship. It was not uncommon for him to browse for three or four hours at a time most days when he had work and "better things to do".

He did not understand his compulsion when he was in its grip. Now he realises it was his escape from unhappiness and insecurity. "I could retreat to the security of my fantasy world," he says. "I thought it was relatively harmless. I'd started as a teenager with magazines, but with the internet there was so much more content, it was always available."

After he was sprung, he was devastated when his marriage broke up. He felt like a worthless person. "My wife was a very honest, upfront sort of person," he says. "It was the fact I had been deceiving her for so long that made her so angry and upset."

Now that he is not so controlled by pornography, he worries about young people learning about sex from the internet. "It's a big, wide world out there, people are doing strange things, a lot of it not particularly kind to women," Alex says. "I was fascinated, I wanted to have a look, but with teens growing up this will be their experience."

Whether people can become "addicted" to pornography, as they can to heroin or tobacco, is debatable. Most experts steer clear of pathologising behaviour just because it is not mainstream.

Eric Hudson says people in the grip of internet pornography, who feel they need progressively bigger hits, experience it as an addiction. But they are not physically addicted. People have some control over their sexual behaviour, he says.

Brett McCann says people should seek help early if they believe they are developing a habit that could damage their relationship.

Gracie's ex-boyfriend, when last contacted through his MySpace site, had one "friend" - from an interactive adult porn site. "Some things never change," she says.

Rebecca's fiance, having acknowledged his problem, has remained "abstinent" and life is "absolutely fantastic", she says.

It may not be strictly addictive, but for a silent minority, internet pornography has brought anguish, shame and broken hearts.

Adele Horin is a senior Fairfax writer.