If you think your friend is falling for your boyfriend, you should talk to her about it. Ask her why she is falling for your boyfriend. Give her a chance to explain herself and avoid getting mad. You should then talk to your boyfriend because he might be leading her on.
Hint ur friend that how well he treat u and if they really r ur bff then they wont go for ur boyfriend/girlfriend. And then make sure u know where ur boyfriend is at all times this way u can make sure he isnt cheating on u.