Try to stop liking her... I know that may be a hard task, but what else can you do? Talk to her as a friend, and not a love interest. Eventually you won't have a crush on her, but that will fade within time.
Then she has to choose you or her boyfriend.
Does the girl know you like her? How long have you an and your boyfriend been together? And are you asking what should you do?
Try an show her how cool you are compared to her boyfriend
If he is her boyfriend, hopefully, she would like him.
Wait till she doesn't have a boyfriend or move on
Treat her better than her boyfriend does.
You get beat up
Find a way to impress her.
It means that they like you more then they like there boyfriend
fight the other kid and take the girl
Move on, she's taken.
you make a girl jealous and the girl will hate her boyfriend and follow you as her boyfriend and listen to that song Justin bieber one time