dj357 wrote:Well that one is a tad obvious

I was more wondering specifics such as lack of sexual intimacy, loss of emotional connection etc... It would also be very interesting to see a breakdown on the gender percentages. My gut feeling is that men would be more prominent on the list but one never can tell.
I wouldn't be so sure men lead the list. They certainly bear the burden/enjoy the benefits of a reputation for being dogs when it comes to sex and commitment, but let's face it-- these men are cheating with someone, and I doubt Lordpasternack can keep up with the whole demand.
I think the reason it's often called cheating is because people feel a similar thrill of getting away with something secret and taboo as they might shoplifting, or winning money by cheating at cards. The thrill of trying to get away with something heightens the sexual thrill. Of course, there could be any number of influences at work-- feeling neglected/undesired by one's spouse, falling out of love but unwilling or unable to change the bad situation in a more forthright way, falling desperately in love/lust with someone else, and making a bad decision under the intoxicating influence of those emotions.
And I'm sorry, but cheating on someone is a bad decision. It's lying to someone you at least at one point respected enough to enter into a commitment with. This is a separate issue from whether or not that sort of decision is anyone else's business, and decidedly a separate issue from open relationships, French marriages, polyamory, etc., which are agreements of different sorts, that don't involve promising someone something and then breaking that promise secretly.
As for doing away with marriage, why is that necessary? If you don't want to be married, don't get married. That seems simple enough, and doesn't involve depriving other people of a lifestyle they're happy with.