My Friend has changed a lot..?

ive had the same problem! im 15, and i used to have a really good friend, but then once we turned about your age she began changing. she was ignoring me for guys in the hall, and getting involved with older guys. She was being mean to me and i really didnt want to be her friend. i finally had enough and i took her aside and simply told her "youve changed in a bad way, and if youre gonna be like this all the time i just cant be friends with you anymore" after that i just walked away. she kept trying to be friends with me, but she hadnt changed, so i just didnt respond to her texts and tried to forget her completely. i can honestly say, once i forgot her, it was a big load off my shoulders. she obviously wasnt the friend i thought she was, and it was really great to finally be free of her. my advice to you would be to try and do the same, because it obviously isnt doing you any good to be around her. try hanging out with people that will help you and encourage you, instead of bringing you down. i think it will really be good for you. Hope i could help!