The biology of monogamy
When the men received a nasal spray of oxytocin—which is released by the body during sexual arousal—they rated their partners more highly but not the other women. MRI scans show that after an oxytocin dose, areas of the brain associated with rewards, which also drive drug addiction, were more active when the men saw pictures of their partner, the researchers report online today in the Proceedings of the National Academy of Sciences. The finding could help explain the biological roots of monogamy in humans: Being in a long-term relationship raises a person’s oxytocin levels, which in turn increase the psychological reward of spending more time with that person. The cycle, the team concluded, could literally lead to an addiction to one’s lover.
Essentially, the research found that oxytocin release during climax contributes to romantic bonds in men by enhancing their partner’s attractiveness and reward value compared with other women and, even when not in a sexual encounter with her, exposure to oxytocin will still trigger the exact same mechanism towards only the primary partner providing him with that oxytocin release.
I suspect that the same is likely true in women.
What this really says is that marriage IS fundamentally a sexual pair bond and, when a member of a couple uses the witholding of sex as a means of control, all s/he accomplishes is an undermining of the mechanism designed to make each seem desirable, beautiful and lovable to the other.
When sex is thrown under the bus, the only prize you win is making your partner no longer addicted to loving you…