Who's Cheating on Who?

I just saw an episode of "Cheaters", a show dedicated to the "art" cheating on a spouse, fiance', or other respected person and not wanting them to find out. On this particular episode a young woman (we'll call her Amy) confided in "Cheaters" producers about her suspicions of her husband (we'll call him Mark) cheating. I'm thinking in my head, "If you suspect him of cheating...chances are he probably is." So the "Cheaters" crew followed him around for a couple of days and noticed that this man was turning out to be clean. He went to work six out of seven days, didn't have any unusual phone call conversations and came home to his wife on time everyday. What was this woman's problem? Well on one particular day, "Cheaters" decided that enough was enough and decided to call off the investigation (it was leading to nothing). As they pulled into the parking lot of the local Wal-Mart, they noticed Amy and Mark's truck parked in a secluded area (by the dumpsters in back) and said we got him. Funny thing is, the person in the back seat of their 2005 Tahoe wasn't Mark...it was Amy with another woman. Who just so happen to walk outside of the Wal-Mart and around the corner to see what's with the TV camera and crew? You guessed it...Mark. I thought this was the best episode in "Cheaters" history. During the confrontation segment, Amy couldn't explain anything...she was completely dumb-founded. Mark must have asked 20 million questions because his lips were moving at an alarming rate. Amy attempted to explain herself, but couldn't seem to get the words out of her mouth. I looked on in amazement. I couldn't believe it. I just don't understand why she did what she did. Not the cheating itself, but the calling "Cheaters" to investigate whether or not Mark was cheating...he's the victim. Who would've thought the accused would turn out to be the victim. I just had to right this down because it was the funniest thing I'd ever seen on "Cheaters".

Which brings me to this question...why do people cheat? I'm not going into the whole "Who cheats more" or "Who's the better cheater" Men or Women?" crap...that's only gonna cause an argument! But knowing how people are, someone is gonna respond to this and tell their story about how some guy/girl broke their heart and that the men/women cheat more.