WHO'S THE BAD GUY IN THIS SITUATION?

If you are not bf and gf then he is open game but if she like him first and you knew about it then put yourself in her shoes if that is your best friend. One of my main rules is my friends girlfriend or girls they like are offf limits.If he wants to be with you he should tell her that . How do you know he doent like her did he tell you that?If he did he should tell her too.does he know that it is causing a problem between the two of you?