I wonder if that's why there's so much divorce...people think there's something wrong with them when the moonbeams go away and the butterflies drop dead. At that point the rubber meets the road, so to speak, and the hard work of getting to build a true, deep partnership begins.
Its the hard work, notwithstanding the reason it becomes necessary, that is the problem for modern Americans. Our lives are so easy, starting in childhood, that we're simply not prepared for something as difficult as building a strong marriage. Many of us literally
lack the strength to accomplish it because we never did the "exercises" that would have built that strength. We have the same problem at work. It's gotten so bad that even the people who percolate to the top of the corporate ladder don't have what it takes to make difficult decisions. Just look at the bozos who thought it was okay to institutionalize subprime mortgages: Wow! Quick profits! They didn't bother to extrapolate a mere five years into the future.
The lack of marriage as a system would not preclude many people from choosing monogamy. In fact many people DO choose to be monogamous without marriage.
It's become quite common in Europe. The last statistics I saw a few months ago said that a greater percentage of European children grow up to adulthood in a stable home with their biological parents than American children, even though a much smaller percentage of those parents are married than American parents.
It all depends on whether the relationship grows to continue to meet the needs of the persons in that relationship.
True, but it also depends on whether the participants in the relationship also grow.

A growing number of Americans simply fail to mature in many important ways because our culture not only tolerates it but encourages it.
Just look at the people who make up Congress. They're pounding their tiny fists and throwing temper tantrums, saying, "No no! I won't let you raise taxes/cut spending/increase the debt limit
(pick any one or all three of those and you've described virtually the entire Capitol Building), and I don't care if it destroys the global economy and makes the Great Depression look like a bad day at the beach, because I can't think that far in advance."
I wish I had the reference for this quote, which I got from a newspaper or magazine earlier this year:
People have long made the mistake of saying that America has a cult of youth. What we actually have is a cult of immaturity. Few people are young, and the few anointed Disney stars fall consistently and spectacularly as meteors every year during sweeps season. Instead, we have people like Snooki. You are only young once, but there appears to be no limit to how long you can behave like a five year-old. Some people can relate to teens. Their secret is simple: They are not real adults. They cannot manage their finances or hold a job for more than two years. After they succeed so well in convincing their kids that they are not their parents but their best friends, they are punished by the kids running off and getting impregnated by Levi Johnston.
I would guess inbreeding was not as rare a case as it is nowadays.
Still, it was less common in our species than in our closest relatives. A primatologist once said that inbreeding is so intensive in gorillas that if you showed a skull from two individuals from opposite ends of the species's range to a biologist unfamiliar with gorillas, he would insist that they must be from two different species.
How would a community like that ever get started and why has it survived over time?
There are still a few Paleolithic and Neolithic tribes left in central-northeastern Asia. These people are living the way their ancestors did twelve thousand years ago.