^For some of us it works straight away. For others, like me, where I am in my development, I need a bit more variety, experience and freedom.
I aspire to have an open monogamous relationship, but I don't worry about it, as I am attracted to a whole lot of people and a whole lot of people are attracted to me - I never have to marry if I don't truly find the right person...and that's OK.
Our mammal side leads us to be polyamorous by nature, but our human consciousness goes more towards monogamy - it's not entirely a social construct, or one of oppression and establishment bondage (but it can be) - when we feel we need wide variety in terms of lovers - this just indicates that in our development, a monogamous relationship is not for us, until we have had more experiences, fulfilled more fantasies, and "lived a lil".
I do, however, highly recommend tantric practices to anyone with a FWB/partner they have seen for a while, and are looking elsewher for variety - indulge in more sexual positions, and practices, instead of a variety of lovers - otherwise apart from those odd rare encounters - you will find it difficult to attain truly divine sex, because you are channeling energy into more than one place, and no one place gets enough to make it a truly worthwhile expenditure of energy.
This is written, and this is also from my observations from my sex life the past 10 years. Try it before you knock it, if you don't like what I am saying, and reap the rewards.