From a purely ethical viewpoint, you should kill them. This kind of immorality cannot be tolerated and persons demonstrating it are entitle to summary destruction.
Don't go out of your way...
That's hard but you should just tell them. If you don't then you could lose him or her for good: Friend or not. You may lose them as a friend and you definitely don't want that to happen. Just tell...
he is a player and if he is not willing to give up the other girl for u he is not worth it That should be fine unless one or both relationships are supposed to be committed relationships. Dating...