If you are a female married or dating a male and fool around with a female why is that not cheating?

Who says it's not cheating? Cheating is the violation of a commitment between two people. If you tell someone else that they're your "one and only" when they aren't, that's cheating.

a man may not consider that cheating (even though Rob^^ makes a good point) because as a male, his primal worries are that some other MALE might try and steal his lady, so some more primitive-minded guys might not think it "cheating", per say.

I agree with Rob... and lbk_princess's theory, too. Plus, I think there's still less value placed on female-female relationships, so they may not consider it to be on the same level as a "real" male-female commitment. Some see it as just "playing"...

It's totally cheating but not many consider it cheating. I know a lot of bisexuals that have a girlfriend and a boyfriend at the same time. I think in their mind they don't consider it cheating but having the best of both worlds.