What I would do is tell him that she is cheating and give him some good proof and if he dosent want to believe you then that's his choice. Hey! You warned him!
Yes you should tell her that he is cheating. Because later, it will hurt her if not told.
Cheating
You should tell your friend that he is cheating its best that she knows.
dont tell your best thing anything. If you do you will lose that friendship forever. I would just tell the person that is cheating to dump his girlfriend so you dont have to worry about it anymore
you should apoligize t your friend and his girlfriend
SHOW him that she is cheating. if he knows that you like him, a simple "shes cheating" wont make him understand.
you tell him and ask if your really best friends, because best friends should never ignore you
That really is a grey area. Of course it always best to tell someone when such behaviour is taking place but just be sure you have her best interests at heart.
You would not like it if your best friend cheated on you with your boyfriend so that is not a nice thing to do to your best friend. First, you should stop saying you are best friends with the girl when you are 'cheating" with her boyfriend. Best friends do not do that. Second, you should stop going out with her boyfriend. Third, you should tell the girl that the guy is cheating on her, even though you will need to tell her that it is with you. If he does it with you, there is a real good chance that he would cheat on her with someone else. Finally, both of you should dump the guy.
If u want to be slapped
Best friends are best friends because they share similarities. Lazy or hopeless guys love their best friends' girlfriend because he would like the same kind of girl.
Grow up, please. If you like your best friend, you don't love your girlfriend. You girlfriend cheating on you is not reason or justification for you to do it back. You didn't like being cheated on, did you? So why would you do it back? You obviously forgave her & tolerated it. If you can't, LEAVE YOUR GIRLFRIEND. Do not go out with your best friend if you're not single.