Lust?

That's actually a common misconception. Most people believe lust leads to infidelity and that is the number one reason for divorce. It is one of the top reasons (#2 as a matter of fact), but the top cause of divorce (in America anyways) is a couple's inability to cope with or manage unified financial tensions. In other words, the number one cause of divorce in America is $$$$$.

I'm not really sure whether or not I agree with that. Usually, I think people just grow apart or learn that they're not compatible. As far as how marriages start, I guess they are usually love-matches. Many of them are still arranged, though.