If there's one thing most of us can agree on it's that sex and longterm relationships always seem to nose-dive into catch-22 territory. In the early days you and your man would've generated enough sexual electricity to keep a hotel room powered for days. Fast forward a few years and while your commitment and love have deepened, that heady La-Perla-thong-ripping passion has simply withered away.

According to Esther Perel – a New York based author and the world's leading authority on sexlessness in relationships - a lack of sex and monogamy has always been a somewhat impermissible truth, and it may now account for rising divorce stats in the UK. In her highly acclaimed book, 'Mating in Captivity – Sex, Lies and Domestic Bliss', Esther puts forward this refreshingly honest thesis: stable, life-long loving and sexual desire are largely contradicting energies, and, 'Couples who may have had great sex to start off with find it shocking how things unexpectedly go off track once domesticity sets in.'

Ah, domesticity. Sharing the washing up, clipping toe nails together in front of the TV, weekly shops at Sainsbury's. As creatures of habit, these benchmarks are usually bonafide signs we've reached the highly sought-after stage of cosy coupledom. But why does sex go from hot to distinctly not whenever we get comfortable with a man?

'Romantic love flourishes in being close to your partner, in worrying and feeling responsible for them,' says Esther. 'Yet for many, these elements block what's needed to fuel their erotic desire. If love thrives on familiarity and security, sex is all about surprise and insecurity, mystery and risk. Love is about having; sex is wanting.'

What's needed, Esther argues, is a way in which we 'can reconcile the need for a safe and steady relationship with the wish to have novelty and excitement in the bedroom.'

Before 'Mating in Captivity', many self-help sex manuals insisted the way for a couple to recapture their early sex bond was to build on intimacy levels. Esther's approach is wildly different. 'Greater intimacy – such as in over-communicating verbally - doesn't always lead to better sex,' she says. 'Desire increases when you have space and a sense of autonomy so you can be freely passionate and lose yourself. It's selfish to an extent. It's about allowing yourself not to worry about the other person, about being your own person - like you were at the start of the relationship.'

Esther points out how much we fancy our partners when they're doing something not connected to us. Like how gorgeous he suddenly looks when he's playing tennis or talking in a crowd. 'In those moments you're not the centre of his thoughts, and it's his separateness from you which heightens your attraction,' she says. 'You long for him because he's out of your reach. Seeing your partner in the way a third party does reminds us that no one ever belongs to us or knows us inside out. It makes us suddenly feel possessive and less likely to take them for granted.'

The spontaneity myth
'Many of my patients claim they simply can't be pre-meditative about sex because it's something that just happens,' says Esther. 'But sex isn't ever spontaneous. In the early days you secretly planned to have it whenever you carefully chose what perfume, dress, lingerie to wear. We forget how much groundwork and preparation goes in. So now you've got to make it happen again like you did back then. Committed sex is always intentional sex. When you plan something you're putting effort in to it which means you value it. It's an important message when reaffirming your desire.'

Challenging times
Pressure is a passion killer. Those 'have you done this, tried that' conversations too often translate as you 'should' be doing this and 'should' be trying that. Such complications blur what sex is really all about: truly enjoying ourselves. 'Sex as such a public thing hinders our own fertile fantasies,' says Esther. 'It stops you from really knowing what's sexy for you. A person's sexual pleasure should be a product of their own imagination. I tell people to tune into their fantasies. It's risk-taking without harming yourself because you're allowed to think and feel things you normally wouldn't - for example, if you're someone who is dominant and leading at work you can be submissive and surrendering during sex.' Ultimately Esther's thinking behind her book is this: to preserve a sex life, you've got to give it sufficient attention and want to bring it back. Readdressing the void between love and lust is a delicate balancing act, but as Esther concludes: 'The only sex worth having is sex worth wanting.'

Here Esther shares a few practical wisdoms on how to get lust back:
'Create psychological distance from your partner. Go out with friends, and maintain your own interests. It's about being mysterious to someone you are familiar with.' 'People settle for what gets them results in the bedroom. But when you know what you're going to get and how you're going to get it, lovemaking becomes routine and dull. You must play with your imagination, experiment and reinvent yourselves.' 'If you don't want sex to be another "to do" on the list, treat it as a priority. Book yourselves time away or make time at home. It's not an instant guarantee you'll have amazing sex, but it's a start.'

Mating in Captivity, £11.99, (Hodder & Stoughton) by Esther Perel is available to buy at bookshops nationwide.