even though fewer premarital sexual partners produces a higher marriage success rate

This is probably the most obvious example of selection bias ever.

What you're actually sampling is the devoutly religious, who believe divorce is wrong. No shit it has a higher success rate. (but still very low, and not counting other negative outcomes like a dysfunctional relationship and abuse from the woman)

There is no magic virgin who will love you forever. Look at all the high school sweethearts who ended up in bitter divorce battles.