High fidelity

Was I the only 20-something woman in America who thought Miranda was a complete idiot for moving out on Steve after he confessed to his one-night stand? Probably. There's a lot of anecdotal evidence (and a fair amount of actual research) showing that Americans are much more moralistic than Europeans, Latin Americans, or many other societies (setting aside ultra-religious societies like Saudi Arabia or Afghanistan) when it comes to extra-marital sex. most of the comparisons are between the US and Europe, in part because that tends to be the region Americans know best but more importantly because gender equality is roughly comparable on either side of the North Atlantic.
This New York Magazine article by Philip Weiss is a compellingly honest account of one man's struggle with monogamy. Some of the intercultural highlights:

When I decided to write about it, the novelist Frederic Tuten offered a warning
about the sanctity in which Americans hold monogamy in marriage. “You can go
against it in life, but don’t speak against it. It makes you a monster. Who speaks against it? And this creates a dichotomy, between what we live and what we profess.”

Apple pie, motherhood and monogamy: 3 core American values?

Braverman pointed out that American habits, even on the Upper East Side, have a
moralistic component. That affects men too. “I’m not a sociologist,” she cautioned. “But we have a history of puritanism as a very dominant sensibility in the United States. That’s not the dominant sensibility in France or Italy. My observation is that often when people are having an affair, they get very involved and they start questioning their attachment to the marriage, whichbecomes very threatening to the marriage’s survival. The husbands here don’t treat the affairs in the way we imagine Europeans treat their affairs.”

This passage explains particularly well, I think, how rapid cultural change in our society has left us searching for new models:

Susan Squire, the author of a forthcoming history of marriage called I Don’t, told me that marriage wasn’t made to handle all the sexual pressure we’re putting on it. For one thing, the average life span is far greater than it was 100 years ago; what is marriage to do with all that time? And in days gone by, marriage was a more formal institution whose purposes were breeding and family.
Squire says that cultural standards of morality have changed dramatically. In ancient aristocracies, rich men had courtesans for pleasure and concubines for quick sex. In the Victorian age, prostitution was far more open than it is today. America is a special case. By the early-twentieth century, she says, the combined impact of egalitarian ideals and the movies had burdened American marriage with a new responsibility: providing romantic love forever. Squire says that the first couples therapy began cropping up in the thirties, when people found their marriages weren’t measuring up to cultural expectations.
“Marriage isn’t the problem; it’s the best answer anyone’s come up with,” Squire says. “Men and women are equally oppressed by expectations. Expectations are ridiculously high now. Nobody expected you to find personal fulfillment and happiness in marriage. Marriage can be very satisfying, but it’s not going to be this heady romance for 40 years.” Marriage involves routine, and routine kills passion. “What does Bataille say?” Squire continues. “There is nothing erotic that is not transgressive. Marriage has many benefits and values, but eroticism is not one of them.”
A long and supportive marriage may be more valuable than a sexually faithful one, Squire says. “Why does society consider it more moral for you to break up a marriage, go through a divorce, disrupt your children’s lives maybe forever, just to be able to fuck someone with whom the fucking is going to get just as boring as it was with the first person before long?”

My perception of the French (or at least Parisian) attitude is just what Squire seems to advocate: the right thing to do, in most cases, is to stay together for the kids, the family, the social life, and yes, money, and eventually work it out to grow old together. I know several couples now in their 40s and 50s who have had aventures and rencontres over the years, but at the end of the day still very much want to be married to one another.
One man interviewed for the NY Mag article is Glyn Vincent, a New York writer on social and cultural matters who is half-French:

“Marriage is more of a formality; sex is not the most important thing,” he said. “From the time I was small, I was led to understand that people have affairs. C’est la vie. This is just going to happen. You’re not going to make a big deal out of it when it does happen. You shouldn’t be hurtful about it. You’re going to be discreet. Don’t shove it in people’s faces.” While Vincent sees young Americans experimenting with new norms—“fuck buddies,” friends with benefits, etc.—those innovations don’t seem to have rubbed off on their elders. New York divorces continue to involve sexual infidelity as a breaking point.
“When I make a comment about infidelity in social situations, there’s always a
little element of mistrust in people’s eyes,” he said. “I think we’re getting into a question of social stability. The male libido is considered a very dangerous and a potentially disruptive force in society. I think that’s why there are so many religious dictums and taboos around that. The idea that one is allowed multiple partners—this is something that has to be rigidly controlled.”

Not having any experience with long-term monogamy myself, I'm loath to make a definitive judgement on these issues. That said, as the child of a 17-year-long faithful (according to each of my parents, at least) but nevertheless very unhappy marriage, I'm reluctant to equate infidelity with automatic divorce. I guess the only point of view expresssed in the article that I can whole-heartily embrace is this one:

My sister Alice, a respectable suburban woman happily married for eons, says that she’s come to respect the fact that sexuality runs the gamut: Some people seem happy with a sexless marriage, while others aren’t built for monogamy. The only morality she hangs on to is how honest one person is with the other about their stuff going into a marriage.