Why is she using me!!!?

seems like this girl is only playing with your feelings. She doesnt like you cause if she did she would not do this to you its one thing for a girl to flirt to make you jealous (still isnt right) but another thing to start going out with another guy when you just told her you liked her. if she liked you she would hang out with you and talk to you and try to catch your attention. She would not being doing what you have typed. Try to move on for what you feel her because she is only going to play games and use you. Not worth your time, honestly. Let her do what she wants if she wants to go out with that guy well that was her decision, wrong move though. But you continue your road, you are young and can still have other crushes and find other girls who wont play with your heart. Move on or stay tangled to being used.