Wow this is exactly what one of my friends asked me. I told her don't mess with the relationship cause you'll end up losing your chance with the guy and your friendship with the girl. Just wait till they break up (hopefully its a happy breakup, or else you'll have to wait a while) then get your flirt on! If it is a bad breakup then be there for the guy a lot and be as comforting as possible *without ignoring your friend too* this tends to be hard so just keep your friend's mind off the break up and be funny with her, then go to comforting the guy in what ever way you think is best. The above poster gave some great advice! You had your chance and didn't run with it. If you interfere between this guy and his girlfriend he'll lose all respect for you. Generally when young the relationships don't last forever so as the above poster stated wait until they breakup.