Friend leaving me behind?

My best friend and I both started the same new school this year. I began to make new friends, and then she began to make friends, but we still remained very close. Her father died last year, and I have been there for her and supported her throughout all her problems. At school, she broke into a small group of friends and became very close with them after just one day. She slowly began ignoring and avoiding me. I tried to confront her about it, but she brushed it off saying "we could still be best friends and not talk at school." The morning I arrived at school on my birthday, she walked right past me without saying a word to greet her new friends. I really wanted to befriend her new friends, so I started approaching them and I did a science project with them. As I began getting closer with them, my old friend started becoming closer with me again. We all became a very close group of friends, and I forgave my friend for treating me like she did. My new school (a middle school) puts 8th and 7th graders in the same homerooms and some of the same cles, so 7th and 8th graders are often close friends. The friend that had moved schools with me often seeks the approval and friendship of older kids, and tried to make a lot of 8th grade friends. She soon started ditching our close group of friends to hang out with 8th graders during school and on weekends. I think she knew I was jealous, and I think she considers some 8th graders to be her best friends instead of me. I feel like she never wants to hang out with me, and when we do, it's awkward. We have a very special bond and have been friends for a long time. We have shared a lot together and I don't want to lose her. What should I do? What can I do to bring us closer together?