Theres a girl who seems to like me, but i like her best friend, and she has a boyfriend, who treats her badly

theres a girl in my school, called jane* who seems to like me, but i love her best friend mischa*, but mischa* has a boyfriend. he treats her badly, but she doesnt seem to notice or care, and it it makes me really jealous. my best friend john* is smitten with jane* and he will probably kill me if i end up with her.i dont want to turn jane* away, because i dont want to hurt her, but john* will probably hate me if i end up with her. i really dont know what to do. some help please?