On Alternet, in the article "Is Cheating Ever OK", the author addresses the question:
If one partner refuses to have sex, does the other have the right to seek it elsewhere?
My response to this article follows below:
Perhaps the question should be "Should monogamy always be an unquestioned part of every intimate relationship", rather than, "Is 'cheating' ever OK?"
While monogamy isn't natural for human beings in general, some people have an easier time being monogamous than others. The intensity of libido, of sex drive, varies widely among people. Monogamy is, perhaps, easier among those with roughly matching sex drives, and easiest among those with moderate to low libidos, where variety and/or novelty isn't high on their list of sexual needs. With a couple where both partners have relatively low libidos, a sexual dry spell would not necessarily make them want to look elsewhere for sexual gratification. Monogamy tends to work well for such people.
But for those of us with moderately high to very high libidos and/or where variety and novelty is important, monogamy is akin to the restrictor plates that NASCAR uses at superspeedways to limit how fast the cars can go. That is, there's a lot of power (sex drive) being thwarted to keep it within socially accepted limits.
If you've got a couple with mismatched libidos, as described here, you've got a recipe for frustration for the one with the higher libido. Such couples may be well-matched otherwise, but the expectation of strict monogamy in such instances can ruin what was otherwise a good marriage.
Likewise, there are instances where one partner becomes chronically ill or disabled and is no longer able to have sex. Is it fair to expect the healthy partner to satisfied with "just cuddling" for the rest of their lives?
Another related sacred cow is that many people believe that sex and love must always go together; that the only "proper" reason to have sex is as a way to express love for one's partner. But in reality, people have sex for many different reasons in addition to love: to fill a physical need similar to eating, sleeping and so on, a stress reliever, they're horny, etc. I'm of the opinion that as long as sex is between consenting adult partners, there is no one "proper" justification for sex.
In addition to questioning the assumption that all intimate relationships must always be monogamous, no matter what, we need to question the assumption that the only proper reason to have sex is to express love for one's partner. Perhaps then, couples with mismatched libidos or those with a disabled partner who are otherwise happily married, could continue to be happily married without one partner being sexually frustrated.