Complete and Utter Confusion?

Guys, I have a questions for you (when I say guys I don't mean in that whole 'hey guys!' i mean as in the male gender) why is it that you feel as though you can do whatever you wish? I'm just wondering, (and yes, i know girls are at fault for this too but this is not what that is about at the moment) why is it that you feel like you can have a girl on your arm, example the girl you slept with last night, nabbed their virginity, or your girlfriend, why is it that you can have them on your arm and alot of you (not all of you, but alot of you) feel like you have the right to hit on another girl, of flirt with another girl when yours isnt looking? Does that strike anyone else as wrong, or am I just old fashioned? That's always something that has baffled me, always you are with someone and evern when they aren't around you need to have the respect enough to not hit on other girls while she isn't around, and if you don't care about her enough to do that maybe you should think about ending the relationship and let her go so she can start a relationship with someone worth her time. But that's my thought, im probably just being old fashioned.