I asked a question in my last post and G-d decided to answer me when I was browsing a Jewish website today.
My question was: When a man cheats on his wife, whose fault is it - his own for breaking his oath of fidelity, or his wife's for not keeping him happy?
The answer that I found was written by Rabbi Isaiah Horowitz (aka "the Shelah"), a renowned rabbi and mystic who lived from 1565-1630.
The Shelah writes that all human beings have two kinds of desires: desires of the soul, and desires of the flesh. Both are good, writes the Shelah, since both were given to us by G-d; but they have to be used correctly.
Following the desires of the soul, a person will do good deeds, following the path that G-d wants us to follow.
Following the desires of the flesh, however, often leads a person to selfishly chase objects of their own pleasure.
The desires of the flesh were not created for a person's own selfish use, says the Zohar, (the most important work of Kabbalah); rather they were given to each person for the sake of their spouse.
"Therefore," writes the Shelah, "a man should not indulge in any pleasure except that which beautifies and benefits his wife."
The explanation goes into more Kabbalistic (and more complicated) detail, which I won't go into here, but the practical lesson here answers the question that I asked by telling us that a man is only given "desires of the flesh" for the sake of his wife, so if he decides to take them elsewhere, he's using those desires for entirely the wrong purpose.
Clearly, according to the Shelah and Kabbalah (and, thus, according to Torah and G-d,) a man who cheats on his wife (or, conversely, a woman who cheats on her husband,) is in the wrong.