My friend is dating my ex...?

So me and my like best friend (we are practically sisters) are getting in lots of little fights lately. It all started after she started dating my ex boyfriend. They have been dating for like a month and they are acting like they are totally in love with eachother. her facebook statuses are constantly about how she doesnt wanna lose him and she loves him soo much. its unbearably annoying. she also lies to me all the time. we make plans to hang out and she ditches me saying she doesn't feel good, but really she hangs out with her boyfriend. its all immature crap if you ask me. i dont wanna ditch her as my friend becuase losing our friendship over a guy is ridiculous. but i also wanna tell her how i feel without her getting mad at me. what do i do? (i'm also sharing a locker with her so that makes it difficult. and we are freshmen.. so we are 14. idk that might help with your answers lol)