In her fascinating essay on open marriage, Susan Dominus writes:
It took decades for sex researchers to consider the possibility that women’s fabled low libido might be a symptom of monogamy. An entire scientific field, well chronicled by Daniel Bergner (a contributing writer for the magazine) in his book “What Women Want,” has evolved to try to understand the near-total diminishment of lust for their partners that so many women in long-term monogamous relationships feel. One 2002 study found that men and women in committed relationships shared equal desire at the onset of their relationships, although for women, that desire dropped precipitously between one and four years into the relationship; for men, the desire remained high throughout that period. In his book, Bergner cites research suggesting that women desire novelty as much as men. The recent attempts to formulate medication to address waning sexual interest has been predicated on the assumption that one possible response — indulging an interest in newer partners — would never be practical and could be destabilizing.
That explains it. Call me old school but I don’t see open marriage is an option.