How can i steal this guys girlfriend?

i think shes very pretty and i sort of think she finds me attractive , not sure though. Ive been hanging out with my cousins friends and i like one of the girls who has a boyfriend. During the few times ive hungout with them i would just be standing their and she would pull me over to dance with her, we would bullshit about t.v. shows. just normal stuff. I wanna know how i can outshine this guy and get her more attracted to me.How can i steal this guys girlfriend?
i don;t think it's right to interfere with another person's relationship. If she likes you, then she will like you and leave him, but there is nothing more you can do to outshine him, just be yourself, you don't want to be someone your not. girlfriend/boyfriend stealing is shallow, and don't let her look at you that way either.