Don't do something like this, that is VERY dangerous because it could RUIN the best friend relationship in an instant! Assuming you're calling the best friend a 'best friend', I'm going to assume that the relationship if close if not very close, doing something like this to him or her is crazy because it could hurt them A LOT.
ask them,
Don't go there! He is going out with your best friend. But then maybe you to belong together as you both are lying to her.
She likes you and that other guy and her boyfriend but does not know who she likes best.
Know what he likes before you get him somethig
a way to know if he likes another girl is if he keeps looking at her and smiling also if he talks about her with his friends.
Well think of it this way: Who is more important to you? Your best friend or your boyfriend's friends?
If your boyfriend likes your best friend he is always around her, and only is around you when your with her/him. If he asks "Is Alice there?" And you say no and he doesn't come.. Or if you say yes and he does.. Then, you know he likes her.
At least you know she likes him. I would try to keep them separated. Hopefully you trust your boyfriend. Hopefully he wouldn't be tempted to cheat on you.
what does he do?
If he seems interested and keeps asking if you and your friend could hang out together then that means he likes your friend not you, what boyfriend would want to be with you AND your friend?? A real boyfriend that likes you would want to be alone with you, he wouldn't want to be with your friends or even his friends.
don't
if he is spending less time on u or if he is really good friends with your best friend and he calls her more than you and your best friend (BACKSTABBER)tellsu she likes him then u know something is going on...................okayyyyyyyyyyyyyyyyyyy!