Long-term relationship is associated with decreasing sexual desire, frequency and satisfaction in both men and women. As well, relationship length is associated with increased risk of sexual dysfunction. The increase in sexual motivation resulting from the addition of a novel sexual partner has been the focus of a large number of animal studies including male rodents, chimpanzees and fruit flies. Experimental studies in humans showed consistently habituation of sexual arousal to erotic material. Repetitive display of a single erotic slide resulted in less subjective and physiological sexual arousal than exposure to different and novel slides. The presence of novel sexual partners in sexual fantasies, and the frequency with which extra-marital relationships occur, is also consistent with the importance of novelty in sexual desire.

On the other hand, most men and women by the age of 40 will be married, in order to achieve safety, permanence, a better care for offspring and pooling resources. Such a social monogamy is generally accompanied by the expectation of sexual monogamy. Is it possible to combine a happy long-term marriage that keeps sexuality alive?

The role of the dopaminergic reward system, attention, psychiatric disorders and socio-cultural factors will be discussed.