Fundies have a higher divorce rate

Or apparently so, though these things are hard to measure. But even if fundamentalist divorce rates are no higher than the rest of the country, they are certainly no lower.
At Pandagon, the commentors are kicking around a number of reasons that fundie marriages might be more set up for failure than other marriages. As can be expected, there's a number of smarmy jokes about not having sex before marriage. But odds are that fundamentalists take the injunctions against premarital sex even less seriously than injunctions against divorce.
No, it's probably alot more complicated than a rash of people rushing into marriage in order to relieve sexual frustration and then waking up the next morning, realizing it was a mistake and getting divorced. That fundamentalists are likely to marry younger probably doesn't mean that they are rushing into marriage to relieve sexual tension. From what I remember from living in the Bible Belt, marriage is the defining event of adulthood. And most people aren't willing to wait until 26 or 27 years old to get accepted as real adults.
Outside of external factors like poverty rates and geographic issues, I really do think that the fundamentalist religion tears at marriages itself. First of all, there's the pressure to marry young. And, as some of the Pandagon commentors pointed out, there's alot of gender warfare going on in conservative Christian circles. Many, many women I've met who follow that faith chafe under the multitude of restraints put on their character and behavior and they don't even have a husband to talk to about it, since the husbands are the primary enforcers of "proper" female behavior. I know when I suffer from some ugly treatment due to sexism, I have my boyfriend to sympathize with me, and that's a source of strength. But the sexist relationship model creates a breeding ground for resentment and dishonesty.