best friend?

Alright, Last tahun was my first tahun of high school. I was really excited and nervous at the same time. As soon as high school started, almost everyone I knew changed completely, except for my bff. Most of the girls in my tahun would talk about boys, trying to make their skirts a little shorter and who should go out with who. My bff and I stayed the same. We would tell each other secrets, talk about the most Rawak things and always laughing together, just like we did in primary. Soon at the start of term 3 she started hanging out with this group of girls. They were nice and funny, but they would talk about the disgusting things (hope anda know what I mean!), try to be cool and talk behind peoples back. After that my bff left me and changed from an innocent girl who is always dressed perfectly and nice to everyone. Now a girl who wears heaps of make up and bugs people around her. I miss her and it hurts so much to lose someone that can make anda smile everyday! I have other good friends, but they aren't as close as she was. I sometimes feel really lonely without a Best friend, so during my free time I would study and focus on school work, and its slightly getting boring. What should I do? thank you...... :)