If you are close to this guy then you should just let him know how you feel and if he continues to go out with this other girl you should just move on. Hope i Helped!
If you like a guy and he has a girlfriend then you should back off and only try and be his friend.
If the boy has a girlfriend, find a guy that doesn't have a girlfriend.
wait
...
He has a girlfriend. So you butt out. It's not complicated.
you use his girlfriend like a ladder and jump over him
Well, its ok for them to hang out. If you trust her, then yes, if not then go with her. Like a double date.
You shouldn't flirt with him if he has a girlfriend.
Spy on him! A wife caught a guy redhanded giving nude photos of himself to his girlfriend.
You simply ask him.
you can tell him, or his girlfriend if you are friends with her
Yes.