But those whose sexualities — whether that means their libidos or orientations or preferences — are mismatched with their partners' understand that relationships are not one-size-fits-all. "The mismatch of sex drive is a common reason why people consider ethical non-monogamy, for sure — I both know and work with couples like that," relationship coach Effy Blue tells me. "Sexual fidelity is not the measure of the success of a relationship. If one party has a higher sex drive, it doesn't mean that the other has to feel under pressure to satisfy. The couple can make a decision together for the harmony of the relationship."And there, again, is Tenet 2: Talk with your partner, as Khan did when she introduced the idea of incorporating sexual non-monogamy into their marriage. Her husband didn't happen to be interested, and that's fine — but Khan recognized ethical non-monogamy as an option that might help satisfy their needs.And that's what we're not talking about when it comes to marriage, and relationships in general. There are more options than we acknowledge in public, more options than we are led to believe. We already allow that sexual orientation lies on a spectrum; it follows that in the vast space between asexuality and hyper-sexuality, sexual desire does, too. There are countless reasons why someone might lose interest in sex or even develop an aversion to it, as Khan did, and I don't pretend to have insight into her physical or hormonal or psychological profile. Anything from medication to mental health problems to fatigue to hormonal changes to sexual history to relationship issues can wreak havoc on a person's sex drive, and many of these can and should be addressed.But, these factors aside, each person's libido is unique to him or her, and you might reasonably find yourself in love with someone with a very different vision of how often you two should get down. "I work with a lot of couples with mismatched sex drives, and occasionally the mismatch can be so extreme that one partner will suggest opening up the relationship," sex therapist Vanessa Marin tells me. "Opening up the relationship can work, but both partners have to willingly agree to the arrangement. It's not going to work if one partner pressures or guilts the other into it, even if it's the lower-drive partner trying to pressure the higher-drive partner."