The third stage, as described in the book entitled “Why We Love” is called the “bonding” stage.  When couples are engaged in the Erotic stage, their brains produce a chemical that makes them “bond” to their mate.  And, this chemical stays in their systems long after the erotic acts have taken place.  Plus, the more sexually active that you are as a couple, the more bonding chemical is produced in your brain.  And so the circle starts.  The more sexually active you are, the closer that you are to your mate. And the closer that you are to your mate, the more sexually active you are.  And so, this spins on into “happily ever after.”