Im so confused and mad with my best friend?:(?

Just tell her. This happened with me and my best friend, because he was getting super annoying and isn't even as mature as a 5th grader yet as a junior in high school. Plus he smokes, which he tries to push on me and im too good at sports to throw that down the drain. You may just be growing apart like me and my friend did, and that's what happens when you get older. Unless she has a serious problem with you i dont see how you guys wouldn't be able to work it out and all three be friends. Just tell her how you feel.