Big friend problems? PLEASE HELP!?

okay, so there's this guy (andrew) who i know my friend likes.. but i like him too.. he likes both of us, which makes it harder.. but see, she has a boyfriend.. She thinks that if she likes a guy, or has ever been out with a guy, he is hers. In her mind no one can go out with him because they would be stealing him from her. She flirts with tons of guys, including Andrew... he like us both, and she still has yet to tell him she has a boyfriend... Its really bothering me that she doesn't even tell him the truth... and i really like him, so i dont know if i should go for it and maybe risk our friendship.. or if i should give up someone i like and also let her lie to him.. :( i dont know what to do.. All three of us are going to the mall tomorrow to hang out (were also all 3 friends) so.. idk if i should do something there? please help! thankyou...