Do guys feel bad if they flirt with other girls while they have a girlfriend?

yes
at that time they cheat they think they are a girl.What makes it less bad

I answered "yes", because you can go too far with flirting. There 's nothing wrong with mild flirting, but if you push it too far and actually cross the line to acting on it, that's really bad. Then it becomes cheating!

Makes you feel guilty so I try not to do it as much as I can. and it shows in the future. Because people are always watching so gotta be careful what you do!

Flirting is natural! It happens whether you are in a relationship or not. Flirting is more of an ego booster than anything else. The important thing is to make sure nothing comes out of the casual flirting. As in, no exchanging numbers etc.