Is the concept that "love and sex are sacred" such a foreign concept to you? The majority of people don't want their partner banging every person on the block because sex is supposed to be a special bond shared between just the two of them. I'm not surprised though with how sexually liberal society has become that people can't even comprehend the concept of not wanting other dudes to plow your wife.
"Plow your wife?" Yeah, that doesn't sound loving. I was talking about being supportive of your wife/partner exploring and finding greater joy in diversity and loving more than one.
Sex is very sacred in many ways. For me, it is a spiritual experience, "touching the Goddess," as it were. In fact, in my youth, I attended many rites where sacred sex was part of the ritual. In a fair number of those, I was the one chosen to be the one standing for the God in the Great Rite, while a priestess would stand for the Goddess. Yes, sexual congress is a sacred act to me. It is a celebration of life and love, a way to connect on a very deep level.
"All Acts of Love and Pleasure are My Rituals."--Charge of the Goddess, Doreen Valiente
I've also shared deep intimate love with more than one woman, each of whom know about the other as well as being a friend to that other. Believe me, it is possible for some of us to love more than one.
Personally, I see the history of monogamous marriage as steeped in misogyny, largely about male power and possession, whether it be ownership of the woman or as part of the common historical method of a father transferring a daughter to another man as part of a political/economic alliance. Even very recently, we have had the double standard (which definitely shows up here) where monogamy is required of the wife (and enforced with grave consequences still in some parts of the world), but tolerated in the husband. Women were a central force in the rise of polyamory.