Cheating has nothing to do with gender.
In the U.S. anyone who has seen the TV shows "Cheaters", "Paternity Court", or "The Maury Povich Show AKA "You are NOT the father!" is clearly aware when it comes to cheating neither gender is standing on "holy ground".
Even lesbian couples report having girlfriends cheat on them.
Most cheaters aren't looking to replace one relationship with another.
The goal of most cheaters is to hold onto all that is "good" in their primary relationship while addressing their other "needs" on the side.
I believe there are three basic types of cheaters.
The Incessant Cheater
This person gets bored very easily. They view monogamy as being the equivalent of going on a very strict diet. It's not a matter of (if) they will cheat but rather (when) they will cheat. They're always looking a (new thrill). Their motto: "Variety is the spice of life!"
The Unbelievable Opportunity Cheater
This person isn't proactively looking to cheat. Maybe they have a secret crush on someone or a person from their past or stranger they consider to be "hot" (hits on them or makes it known they could hookup). Maybe they're on a business trip or they're with friends who egg them on with peer pressure to "go for it". Essentially this person caves to temptation. This cheater may confess weeks/months/years later out of guilt.
The Discontented Cheater
He or she blames YOU! If you hadn't done or stopped doing something they never would have been open to stepping outside of the relationship/marriage. Essentially they feel they were being taking for granted, neglected, or weren't being made to feel special.
Immaturity and unrealistic expectations can also lead to cheating. For example high school lovers going away to separate colleges and believing they'll maintain a long-distance relationship for 4-6 years.