Here’s an excerpt from my discussion of the all-too-common phenomenon of boredom:
The initial Power of Eros tends to be short-lived. You both have sexual energy and affection to burn in the beginning, so it’s easier to remain on your best behavior for a while. Things are very exciting while your infatuation is at its height, but familiarity and certainty soon take the sharp edge off the experience of relationship. This has nothing to do with character or intention or any kind of moral failing. It is simply a physiological fact of life: any repeated stimulus eventually evokes a reduced response. So there is no way in this world to sustain the energy and romance of a new relationship at its most thrilling pitch.
Everybody knows this, of course. Or perhaps I should say that everybody “knows” it. Because it is easy to pay lip service to this truth while not really believing it, down at the center of our most emotional and irrational selves. We can (and very often do) intellectually acknowledge life’s limitations while still craving the impossible.
There may be actual biological reasons for our all-too-common loss of interest in long-term partners. As I discuss on the Page, nature wants us to spread our genes widely and recombine them with a variety of partners…and yes, this applies to women as well as men. So although women’s sexual desire can more easily be subsumed into things like infant care (which is part of the way she ensures her genes survive into the next generation), they can also be revived by a new man. (And yes, I will be talking about Infidelity soon.)
For more on this, and an introduction to what might be done about it, see the Page: Boredom.