It's about 7pm and I am engrossed in a video of Katy and Mark, a married 20-something couple, having sex. I don't like what I see. Katy energetically climbs on top of Mark and works her way towards orgasm while Mark might as well be lying in a coffin. Katy grabs Mark's shoulders; his hands remain almost motionless at his sides. Her moans grow more insistent; whatever noise he's making isn't even picked up by the microphone.

No, I'm not watching porn (though if it were porn, it would be disastrous). Mark and Katy, who have been together since they were teenagers, are one of the dozens of couples who come to me seeking help with their love lives. Mark claims he wants "rampant" sex with his wife. But, from what I see, he needs to look up the meaning of the word.

I help couples like Mark and Katy by watching videos of them having sex (and interacting outside of the bedroom), then analysing what I see. These aren't Paris Hilton-style tapes; they're videos that force couples to take an uncensored look at how they treat each other. The nuances in body language they reveal - a lack of eye contact here, a perfunctory hug there - hint at much deeper issues in the relationship.

For every couple I've seen on tape, the camera illuminates the contradiction between what they think they do and what they actually do. While Mark insisted he wanted his sex life to sizzle, you wouldn't know it. Even his position - flat on his back - reflected his passiveness. When we noted this on the footage, Mark was floored.

After Katy viewed a bungled bedroom moment - she flung Mark's arm away when he tried to cuddle with her - we paused the tape. I told her I had a secret, then whispered, "Men have feelings, too." She started bawling, and we had to give her a few minutes to collect herself. She had no idea she was confusing her husband's attempt at affection with a quest to get into her pants. This blurring between affection and sex surfaces often, and it's a multi-layered issue...

Another couple, Bina and Mark, struggled with a related issue. Bina, whose sex drive outpaced her boyfriend's, constantly pressured him for romps. What she didn't know, until she saw herself clinging all over Mark, is that Bina was craving simple body-to-body contact as much as a good shag. Bina's preoccupation with sex highlights a similar line of thought among many couples: that simply being a good lover can carry the relationship. You can brag all you want about how well you give oral sex to your boyfriend, but if you act like a bitch all the time, he's probably thinking about somebody else while you're doing it.