Divorce rates among conservative Christians were significantly higher than for other faith groups, and much higher than Atheists and Agnostics experience.
Many guess that this is due to the fact that atheists and agnostics wait to get married, tend to date longer because they don't believe in waiting until marriage, and studies have linked higher education and wealth with lower religiosity.
I'm thinking this actually all comes back to wealth. Cohabiting couples are more likely to end up divorced. If they are living together for the sake of affordability then they can't be very wealthy. Divorce rates correlate to poverty and education level. If it's true that the wealthy are more likely to be agnostics and atheists then it follows that they are less likely to end up divorced. Unlike their less wealthy religious counterparts, they are less likely to experience those other stressful external factors.
Of course, that doesn't change all the hypocrisy that results from people who want to protect the sanctity of marriage forsaking their own marriage vows and ending up divorced more often than the non-religious.