How can I get my best friend back? She is horrible/doesn't listen to me. She is normal when we are alone! Help?

My 'best friend' (Claire) has been off with me for a few months now. We have been best friends for 2 years, we were really close and we told each other everything, always knew how to make each other laugh, never put each other down and always stay buy each other. However recently she has become much more popular than me. She has made a lot of 'cool' new friends. In the last 2/3 months she has been getting annoyed with me over tiny things and she has not been listening to me if i need help or i am worried. On facebook chat a few weeks ago, I would say hi and she would take ages to reply and then if i said something she would just reply with 'coool?' or 'wow?' (obviously sarcastic). It was the easter holidays and she had been arranging to meet with all my other friends, but not me! I was talking about what she was doing and she would never ask if i wanted to come! I felt like i was a waste of space or that they didnt want me in their group. I didnt want to invite myself because i knew there was something odd going on. She was being moody and of hand with me for weeks and i had cried about it several times, until i told her how she had made me feel. When i said this she just said i over react and that she doesn't care about our friendship. I was very upset by this. she is still like this with me, but only when we are with other people! when it is just me and her she is just as she used to be! She is being very hipicritical eg: i ask if she can come with me to hand in a letter or something, she say 'No jodie!! Do it yourself!' then the next day she wants to hand in a letter and she says 'Jodie come with me' and I couldn't say no because she would get angruy with me! I am scared of her, I dont undrestand what has happened to her. She has recently got a new boyfriend, and is having some trouble at home with her parents. Is it linked ot this? But if so, why is she only acting like this with me? She is fine with all her other friends! Please help me get my best friend back!!! Please.