My "best friend"is trying to steal my boyfriend and stabbing me in the back.idk what to do?

So I was friends with this girl since 6th grade and im in 9th gr and shes in 10.in the begining of this year she introduced me to this guy (which is now my boyfriend now) now its the end of the school year and she likes him!!and I had noo fcking idea.she is harrasing him,through txt.asking him out,and CONSTANTLY asking him for pics of his d!ck, and her and her retarted friends went knocking on his door! But he didnt answer. And ik she will walk to his house again..and also she is talking sh!t about me to her other friends! I feel like I was basicilly played..my boyfriend DOES not like her at all!!he ignore all her txts I see it on his phone he shows me it.and shes rlly ugly and fat!!!my boyfriend is disgusted with her.and I dont get why is she doing this to me???i was sooo nice to her and such a good friend.I dont understand???and I dont know what to do if I see her in person. I havnt confronted her im just not saying anything.and now,i think I just met her just to meet my boyfriend,cuz i think everything happens for a reason..im just in shock from all of this