As Ikura mentions, serial monogamy is the dominant relationship paradigm in the U.S. In it, a person seeks out an exclusive romantic/sexual relationship with one other person. When that relationship ends -- maybe after a couple of weeks, maybe after a few decades -- both people move on to seek out new, exclusive relationships. The ultimate goal of serially monogamous dating (at least as it's presented in popular American media and in churches etc.) is to find your One True Love, marry him or her, settle down, and live Happily Ever After.
All of the ladies attending the ball
Are requested to gaze in the faces
Found on the dance cards
Please then remember
And don't get too close to one special one
He will take your defenses and run
So we change partners
Time to change partners
You must change partners
Again
There are, of course, alternatives to serial monogamy as a relationship style, most of which are frowned upon in mainstream American society. Clearly, some people are unable to function in a monogamous relationship, serial or otherwise, for a variety of reasons. Likewise, some folks aren't suited to non-monogamous styles like polyamory because adding more people means adding more risk and complication, and maintaining a relationship with just one person can take up all available time and energy.
I've seen plenty of discussion of monogamy versus non-monogamy (open relationships, polyfidelity, etc.) I've heard many people declare that your relationship style is something you're born to, and you can't be "converted" to polyamory if you're monogamous or vice versa. It's presented as a yes/no hardwired state.
It's the existence of serial monogamy as our dominant relationship paradigm that makes me deeply skeptical that all this is truly an inborn binary state for most people.
Why? Because, if all the people who insist they are hard-wired for monogamy actually are ... serial monogamy would be a great big flaming disaster for most people. It wouldn't be workable. From a biological perspective, a monogamous organism pair-bonds with one and only one other organism during the course of its life. And that almost never happens with human beings.
This is how most of our ladies grew up
At the country club dances
They learned how to handle the boys
Gently but firmly they learned to say no
There were four more young men
Who were waiting in the color and the noise
So we change partners
Time to change partners
You must change partners
Again
Think about it. Who really gets to spend his or her life with the first person he or she falls in love with? I didn't. My husband didn't. His parents didn't. My parents didn't. And you know what? Being a person's second, third, or fourth true love doesn't lessen that love.
If you're monogamous, love someone with all your heart, but then she breaks up with you, or if he dies, what then? You're not seen as somehow more monogamous if you continually pine for that person and refuse to go out with a new person. And you're not seen as less monogamous if you do the expected thing and move on to another exclusive relationship after a while.
And if that new relationship fails, well ... you move on again. Repeat as necessary. Maybe you're still in love with your first, maybe you're not ... but a monogamous person is expected by friends and family to make room in their hearts for someone new and get on with life.
I do know people who've dropped out of the dating scene for a while after a bad breakup. But their celibacy is seldom permanent. Most monogamous people do make the choice to seek out new relationships that meet their needs.
Therefore, I submit that many people are more flexible when it comes to fidelity than they realize. It's not a binary world where people are simply black or white, short or tall, straight or gay. People come in all shades and shapes. Desire and need come in all forms.
And most of all? People are adaptable. You change or you die.
All of the ladies attending the ball
Are requested to gaze in the faces
Found on the dance cards
Please then remember and follow your list
'Cause the dear things get hurt
And the broken hearts make you feel
So we change partners
Time to change partners
You must change partners
Again
Lyrics from Steven Stills' "Change Partners"