Hi Ciara Louise, relationships are hard, and it is easier to lose friends than to make them. It's a pity that your best friend has started to grow away from you, but sadly that happens, and you have to try and make the best of things. If you can keep telling yourself that it is not because of you or anything you did, but just because people grow apart. Make friends where you can, and try not to trust people too quickly, or rely on just one friend, especially while you are still at school. The more friends you have, the better, but don't tell ALL your secrets to just anyone. Are you close to your mum, or your gran - is there someone that you can talk to about all this? It is very hard to be trying to deal with this on your own, but please don't let it get you down - you will have many different friends as you get older, and some of them you will eventually lose touch with, but there will always be others to make friends with. That is just the way life is.
Lots of love, and try to stay cheerful.