A random tid-bit to start.
You want an inconvenient truth? Try this one: human beings are clearly evolved for sex lives featuring multiple simultaneous sexual relationships.
Men, especially, are designed by evolution to be attracted to sexual novelty and to gradually lose sexual attraction to the same partner in the absence of such novelty. The so-called Coolidge Effect is well demonstrated in social mammals of all sorts, and is old news to anyone knowledgeable about reproductive biology.
Holy shit! This means I'm normal!