I think that this is where equality of the sexes will ultimately destroy marriage.
Guys like sex, and lots of sex, with lots of different girls. It genetic. This is a fact. Anyone who says otherwise needs to get his testicles back from his wife.
Marriage has worked for so long because men were the dominant sex and could have affairs without recourse - it wasn't that long ago that divorce was literally unheard of! Women put up with cheating husbands because they had no options. Couples stayed together because of societies expectations, long after the guy was sick and tired of his whinging wife!
So either men have to overcome their genetic desire to spread their seed (not frigging likely), or the concept of getting married will change from something that happens for life to something that is a more short-term proposal. This is already happening with de-facto coupling becoming prevalent.