As the evening closed in on their wedding day in May 2005, Sydney PR executive Amelia* felt a mixture of excitement and trepidation. Her new husband Peter* had always been an attentive partner, and had respected her desire to stay a virgin until marriage, but now, the 25-year-old former model was hoping he'd reveal himself to be as loving in bed as out. That night, though, she was cruelly disappointed: instead of the passion she'd been waiting her entire life to experience, "he gave me a kiss on the cheek and turned over," she says sadly.

Although crushed, Amelia reasoned the excitement of their huge Catholic nuptials had taken its toll on Peter, 28, a part-time journalist who was also completing a university thesis. They did make love the next morning - at Amelia's instigation - but it was passionless, quick and unrewarding. As their honeymoon passed with no sex, Amelia became increasingly concerned that something was badly amiss. "He just kept avoiding [sex]," she says. Back home, after "another week of anti-sexual existence" - and concerned by the hours he spent online - Amelia wanted answers.

So, one day, after Peter had gone out, she turned on Peter's computer. She scrolled through the internet history - and what she found left her horrified. A smorgasbord of pornography appeared on screen, with terms like "dripping whores", "school bus chicks" and "virgin fucked" strewn throughout. "My whole life crumbled," reveals Amelia. "I was so stunned, I couldn't cry. It made me question why he married me at all." Worse, she couldn't help but feel Peter had cheated on her. "I felt if he wasn't sleeping with me and he was getting his kicks elsewhere, absolutely it was adultery."

It's an interesting proposition, not least in the light of Australians' increasing use of pornography. Up to 40 per cent of adults use X-rated material, says Fiona Patten, CEO of the Eros Association, adding that Australians spend about $300 million a year on pornographic DVDs. If your partner is engaging in furtive sexual behaviour, and paying to watch other women engage in sexual activity, are they straying into adulterous territory?

At first glance, porn and adultery seem very different. The Macquarie Dictionary defines pornography as being "designed to excite sexual desire" and adultery as "sexual intercourse between a married person and any other person than the lawful spouse". There seems to be a physical demarcation between the two. But in an essay in US magazine The Atlantic last October, writer Ross Douthat gave the issue a different spin. "If it's cheating on your wife to watch while another woman performs sexually in front of you, then why isn't it cheating while the same sort of spectacle unfolds on your laptop or TV?"

And adultery is more complicated than just a physical act, says spokesperson for Women's Forum Australia, Melinda Tankard Reist. Emotional adultery - where a partner secretly shares intimate conversations with someone outside the relationship, for example - is often cited as a cause of relationship breakdown, even though it may not involve a physical transgression. "The feedback I get from women in this situation is that they feel the compulsive use of porn is akin to adultery," confirms Tankard Reist. "They do feel cheated on, and they speak about an emotional betrayal."

To hear the expert's take on porn's effect on a relationship, read the August issue of marie claire - on sale now.

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