I think a big part of it is society in general.

We make the older man into someone more experienced, with more money, and generally more maturity.

We make the ideal age/look for a woman to be about 18 and skinny... which, try as I might, I can't seem to do at 32.

I think it's that each goes for what looks good on their arm as much as anything else. Some people feel better about themselves if others envy who they are with.

I think cheating is wrong and I'm young 19 year old male... I never cheated on any of my girlfriends and I never will... I feel like if your with that person you should only be with that person... cheating is so commen these days hell there's all age's doing it... age don't stop a thing... snf once a cheater always a cheater I just got out this real long relashinship and I still don't see myself dating for a few months... I have to give myself time to I can't think of the word... some finish it off for me!!

But yeah Once a Cheater Always a Cheater... Even if you don't cheat in the future you cheated in the past so you still have that label... thats were the label comes from...

Presently I would say some people cheat because they want more in life while others do it because they are simply not happy in their relationship. They cheat on their partners thinking to get revenge or simply getting that false happiness even if its for a short period.
But, what people do not realise is that they are just putting themselves really down. In fact going a level lower than the partner who is making their lives miserable.
People should try to look for other alternatives to make themselves happy. If they think that being with some one else will make them happy then first leave your partner and then get into another relationship. In that manner, no one can accuse you of being a cheater.