Understanding him properly may require a brief neurochemistry lesson:
The thrill that we associate with the passion of new love correlates with the level of the neuroactive chemical dopamine, the same substance released by the brain during other thrill-producing activities such as gambling or Fluthering. It is the chemical root of all that our brain interprets as intense pleasure. New love, and the sex that often goes with it, are potent stimuli for dopamine release, and we become quite literally addicted to its effect. To keep us from living in a non-functional dopamine stupor, however, the brain also produces a chemical which undoes the effect of dopamine. It’s called prolactin, and its release is triggered by elevated levels of dopamine in the system. Prolactin makes us more functional, but it also makes us feel down and we crave to find that dopamine high once again.
A given love partner will eventually cease to trigger a powerful dopamine release in the other partner’s brain. That doesn’t mean that sexual interest necessarily vanishes (though it can), but the thrill factor is diminished. If, however, a new partner is introduced, hello dopamine! This is called the “Coolidge Effect”, and it’s what drives some to perpetually seek new mates. It’s this dynamic that makes biologists doubt the biological basis for monogamy. We’re fighting the chemical urge to get a new dopamine hit. This can also explain the urge to take up new and risky activities later in married life.
But there is a happy chemical ending to this story. There is another player in this chemical scrimmage called oxytocin. This hormone appears to be responsible for the warm and fuzzy feelings we associate with deep friendship, affection and cuddling. It is not subject to the same wild rises and falls as dopamine, can last indefinitely and doesn’t have the same addictive effect. Unlike dopamine, it calms and reduces cravings. It seems to even contribute to longevity. The secret to a lasting monogamous relationship, in chemical terms, seems to be negotiating the transition from a dopamine-driven new love to an oxytocin-based cuddle-fest. You’ve got to learn to “just say no” to dopamine.