I once heard John Piper say that in forty-some years of marriage he had never been attracted to a woman other than his wife. I remember thinking that Pastor John was either lying or was a most unusual man. Holding him in high esteem I choose to think the latter.
Nevertheless, I think Wendell Berry's writings on marriage and sexuality (recent comments on same-sex marriage excepted) present a more realistic and profound picture of marital fidelity. For in the context of deep rich community advocated by Berry the probability exists of attraction between men and women rubbing elbows in the warp and woof of life together. In a society that worships the values of personal autonomy and self-fulfillment this might be a recipe for disintegration, but in Berry's vision the virtue of fidelity protects the sacred particularity of marriage and the generality of the community. If none of that makes sense read on.
The following is a slightly condensed quote from pp. 122-3 of The Unsettling of America (Sierra Club Books, 1977).
At the root of culture must be the realization that uncontrolled energy is disorderly—that in nature all energies move in forms; that, therefore, in a human order energies must be given forms. It must have been plain at the beginning, as cultural degeneracy has made it plain again and again, that one can be indiscriminately sexual but not indiscriminately responsible, and that irresponsible sexuality would undermine any possibility of culture since it implies a hierarchy based purely upon brute strength, cunning, regardlessness of value and of consequence. Fidelity can thus be seen as the necessary discipline of sexuality, the practical definition of sexual responsibility, or the definition of the moral limits within which such responsibility can be conceived and enacted. The forsaking of all others is a keeping of faith, not just with the chosen one, but with the ones forsaken. The marriage vow unites not just a woman and a man with each other; it unites each of them with the community in a vow of sexual responsibility toward all others. The whole community is married, realizes its essential unity, in each of its marriages.
Another use of fidelity is to preserve the possibility of devotion against the distractions of novelty. What marriage offers—and what fidelity is meant to protect—is the possibility of moments when what we have chosen and what we desire are the same. Such a convergence obviously cannot be continuous. No relationship can continue very long at its highest emotional pitch. But fidelity prepares us for the return of these moments, which give us the highest joy we can know: that of union, communion, atonement (in the root sense of at-one-ment). . .
To forsake all others does not mean—because it cannot mean—to ignore or neglect all others, to hide or be hidden from all others, or to desire or love no others. To live in marriage is a responsible way to live in sexuality, as to live in a household is a responsible way to live in the world. One cannot enact or fulfill one's love for womankind or mankind, or even for all the women or men to whom one is attracted. If one is to have the power and delight of one's sexuality, then the generality of instinct must be resolved in a responsible relationship to a particular person. Similarly, one cannot live in the world; that is, one cannot become, in the easy, generalizing sense with which the phrase is commonly used, a "world citizen." There can be no such thing as a "global village." No matter how much one may love the world as a whole, one can live fully in it only by living responsibly in some small part of it. Where we live and who we live there with define the terms of our relationship to the world and to humanity. We thus come again to the paradox that one can become whole only by the responsible embrace of one's partiality.