There's a website designed for people who are interested in having an affair (I've seen it on Dr. Phil and on Anderson Cooper, so I know it really exists...and it really makes me mad...but that's another topic. To each his/her own).  Based on the membership of this site, they analyzed birthdays to figure out which zodiac signs have signed up the most, therefore making a painstakingly accurate scientific case* for which sign cheats the most.

The results:

MALE biggest cheaters:  Pisces, Aquarius, Cancer
FEMALE biggest cheaters:  Gemini, Aries, Virgo

MALE least cheaters:  Scorpio, Sagittarius, Libra
FEMALE least cheaters:  Libra, Scorpio, Taurus

They've got a full list of every zodiac sign ranked by likeliness to cheat.

I'm a Sagittarius and loyal as a German Sheppard. Never cheated in my life, never will.  Now, where's my Scorpio/Sag/Libra counterpart??

*Clearly NOT painstaking, accurate, or scientific.