And this isn't the first time this girl has been trying to get with a guy who already has a boyfriend. She's even slept with one! And the problem is, my friends boyfriend isn't doing things like blocking the girl, he's even flirting with her back! And my friend knows it too! I wanna go and talk to her boyfriend AND the girl that's flirting with my best friends man but I don't know if that would be a good move... Any advice?