(Marnia) That's an individual choice, but they are certainly an option for most of us. Like it or not, humans are pair bonders by nature. Our brains reward us with anxiety-reducing good feelings in response to close, trusted companionship. This is why socializing, flirting and pairing up appeal to us.
In this respect, our brains are wired differently from cattle, rats and even our closest genetic relatives: chimpanzees. All of those animals belong to the 97% of mammal species who mate and move on, never forming lasting ties. We fall in love because our brains are wired for it. It’s that simple.
Obviously, this doesn’t mean we’re wired for lifelong sexual exclusivity, although many pair bonding mammals and humans do remain sexually exclusive. A practice like karezza can make that a lot easier, assuming sexual exclusivity is a goal. That said, there’s a tension between our bonding inclinations and our inclination to spread our genes around.
In other words, we're also programmed to stray—when novel, willing mates beckon fervently (even digital ones). This tension apparently served our genes over the millennia. We fell in love, at least for long enough to bond to our kids, and then, if temptation knocked, we perhaps did it all again with a new mate to increase the genetic variety of our offspring (and maybe their number).
This tension between the desire for an exclusive bond and the urge to fertilize novel mates has created a degree of instability for millennia, but most cultures managed it one way or another. Incidentally, the capacity to stray does not indicate unlimited capacity for sex. After all, once the evolution of pair bonds allowed human babies to be born with larger skulls, young women could no longer do the parenting job alone with good results. (And fathers no doubt got tired of supporting pregnant daughters indefinitely.) Willing mates desiring casual sex grew scarce.
Male sperm production, and possibly other neurochemical realities, have scaled down accordingly. Human sperm-count data suggests that, in contrast with our closest primate cousins, we are not built for prolific ejaculation. According to author Tim Birkhead, "The rate of human sperm production is lower than that of any other mammal so far investigated." (See: Today’s ejaculation advice may be wrong for our species.)
Most human males also evolved to find bonding behaviors very appealing.
The urge to keep fertilizing if novel mates appear, the Coolidge Effect, is a sort of genetic whip designed to override sexual satiety...even if it does collateral damage to us. It was used relatively rarely simply because opportunities were not plentiful. Thanks to the mechanism that drives the Coolidge Effect, novelty has the potential to lead to overstimulation. It can lead to the need for even more novelty—an addiction process known as "tolerance." Getting hooked on novelty undermines pair bonds because it makes familiar partners seem less stimulating by comparison.
Karezza counters this effect. See An Uncanny Love Potion. It's simply one way to strengthen our programmed pair-bonding urges, and quiet sexual habituation and restlessness. Its major principles have turned up over and over in different cultures under different names.