The first question people ask me when they learn that my husband lost his job, our house went underwater and we went from middle class to barely working poor during the 2008 economic crash is: How did you stay together?

It always struck me as a strange question. But it’s actually a reasonable one. Overall, America’s divorce rate has fallen. But like many things, the poor have not reaped the benefits of this trend. The number of married, college-educated couples splitting by their seventh anniversary has dropped from more than 20 percent in the early 1980s to just 11 percent today. But among the poor, those numbers are stagnant. According to the New York Times, 17 percent of lower-income couples (pairs making no more than twice the federal poverty line of just over $30,000) get divorced, about the same rate as it was in the 1980s.

Why this discrepancy?

To start, money is a major source of tension for all couples (they fight more about it than about anything else, including sex and child care). And less money can equal more problems. Raevan Zayas stays at home with her 1-year-old baby in California while her husband struggles at a low-paying job. “I can’t afford child care to go to work. We can barely afford groceries. Our kid needs new shoes and clothes, and I can’t remember the last time Isaac and I did something nice together,” she said. “Our relationship is so strained. How are you supposed to work through the problems in your relationship when you’re worried about how you’re going to buy milk for your kid?”

University of Michigan economist Justin Wolfers said he’s also found that working-class families have more stringent views about men as providers. The economy has shifted so that those without college degrees have more trouble finding such work, which contributes not only to financial hardship but also to relationship stress. As Johns Hopkins sociologist Andrew Cherbin explains: “I’ve looked at the marriage gap between men with high- and low-earning occupations, and it varies directly with the amount of economic inequality in the country. The more unequal the earning opportunities, the greater the marriage gaps between the classes.”

But financial stress doesn’t explain why inequality, not poverty, is the key to understanding why the poor haven’t seen their divorce rates fall. To understand that, we need to look at women.

Two-thirds of all divorces are initiated by women, according to Bill Doherty, professor of family social science at the University of Minnesota. In the 1960s and ’70s, he said, highly educated mothers got divorced at about the same rate of less educated mothers.

In the last decade or two, these two groups of women have been moving in opposite directions: fewer divorces for graduates, more divorces for non-graduates. In intricate lifetime marriage and divorce studies that span decades, done by Wolfers and Betsey Stevenson, 29 percent of married, college-educated couples have ever divorced. In contrast, those studies show that nearly 50 percent of married couples not holding college degrees have divorced.

Doherty theorizes that the reason for this has something to do with the changing expectations women have for their partners. “What we have is historically high expectations for what young people call a 50-50 marriage,” he said. “People are looking for a high-intimacy, high-income marriage where both partners contribute, regardless of income bracket. Unless you have a good economic base and a certain level of personal maturity, it can be very hard to survive this ideal of modern marriage.”

Cece Azadi of Alabama said the expectations that working-class couples have of each other shouldn’t be unrealistic. It’s not that she needed a man to provide for her, she said, she simply wanted a partner who would work with her rather than against her. “With my first divorce, poverty was an issue, for sure,” she said. “He kept working and quitting, and eventually I realized that since I was the only reliable person in the family making money, there wasn’t much reason to hold onto the marriage.”

Examples like this ring especially true during periods of high inequality. As we came out of the recession, unemployment levels dropped from their historic highs, but more so for women than men. In the summer of 2013, about 7.5 percent of men over age 20 were unemployed, compared with 6.5 percent of women, according to the Bureau of Labor Statistics. The workforce has also polarized, with high- and low-income jobs increasing, and middle-income jobs that men without a college degree previously performed disappearing.

Male students make up just 43 percent of higher education enrollment and 43 percent of current students graduating with four-year degrees. This affects lower-income students more than most as students from the bottom 50 percent of the income distribution in the United States make up only 14 percent of the student body at competitive universities.

Doherty said that as more women show the willingness and ability to work hard in school to try to move their social class, the lower-income men, who previously have been shielded from financial instability with factory and industrial jobs, are being left behind.

“Women around 25 are starting to say: ‘Okay, it’s time to get serious. How do I get to the middle class? What are my prospects?’ And when they realize their partner is not interested in that, they get fed up,” Doherty said. “Plus, many have the added responsibility of a child at home. They can start to feel that they will never have a 50-50 marriage if they stay put.”