The two main neurochemicals related to love and sex are dopamine and oxytocin. Dopamine is the reward chemical released during orgasm, which 1) makes sex feel good and makes you want more sex and, 2) produces the Coolidge Effect or the "orgasm hangover," which makes you sick of the person you just had sex with and want a novel mate. This happens in both males and females.
Oxytocin is also released during sex and is responsible for bonding (though love is a cocktail of more than these two chemicals including adrenaline and serotonin). The primary function of oxytocin is to bond parent and child, however, it also bonds sexual partners (potential parents) and even friends. It increases if parents are going to raise a child so as to keep the parents together long enough to nuture a child until it is biologically self-sufficient (not for life). Touching people also releases Oxytocin and causes bonding.
There is an interesting interplay between sex and love. Sex simultaneously produces a neurochemical to make you want to find a novel sexual partner, but another chemical to also bond with that same sexual partner. These neurochemicals stimulate the release of each other (in a seemingly inverse relationship).
So, the more you orgasm during sex (which is meant to release or prepare the release of DNA), the more likely you'll want a novel mate. The more you have sex while withholding orgasm (which isn't the biological purpose of sex), the longer you'll stay bonded with that sexual partner.
However, this is not a binary situation. You can simultaneously be bonded to a sexual partner and, at the same time, want to find a novel mate as well. In other words, monogamy in humans is a social function rather than a biological function. Your biology says, "Yes, you can have multiple sexual partners at the same time and have an intimate connection with all of them."
I believe that the majority of suffering results from the cognitive dissonance created by social conventions which directly oppose our biology. In order for humanity to evolve, we must reconcile our socializing with our biology rather than fight against it with asinine arguments such as: humans are superior beings, sexual relationships are significantly different from other relationships, and so on.
It is absolutely possible to leverage our biology to make humans into the biggest ballers in the universe. Lets find that path.
*Sorry about not citing my sources, but I've lost the links.
