No you should not. The rumor could not be true and if you don't like them because of what the rumor said. When they did not do anything. The best thing you should do is ask them and do NOT and when I say do NOT I mean it tell who started it or who told you!
It depends, on if they have been doing more and how long..
Yes as long as you tell your girlfriend that you are doing that and you hang out with the girl as if they were friends and nothing more.
i am with another girl friend
Nothing
Because you are not a good best friend and you are an idiot for doing that.
Doing that doesn't make you much of a friend. Does he know how little of a friend you really are?
Because one friend is doing something the other friend is not.
I think you should just see what there doing, and if there just talking forget about it and if the are flirting i would start looking for another girlfriend unless you don't mind sharing.
Unfortunately you shouldn't be doing anything knowing he has a girlfriend - that is just wrong. If he wants to be with you at any time he will leave his girlfriend - if he is staying with her then unfortunately that should tell you something. He may not see things the way you do - especially seeing how he has a girlfriend.
no...but your girlfriend should know where you are and what your doing at all times.
You are not much of a friend to him if you try this. I would reconsider what you are thinking about doing. This is not friendship !
The only reason why she might ask your friend is because you might not be giving her what she wants. Maybe she's giving you a big hint. Maybe you should show her more attention. If you are doing everything possible, then you need to check your with your girlfriend to see what's going on!