It's scary how friends change as you all grow up.

I am in my second year of college now. By now, I had thought that whatever group of friends I have will be the few I will keep for years to come. However, this past summer proved my thinking as flawed.
My best friend from fifth grade, for some unknown reason, as been isolating herself from myself and a few other friends. In a text messaging argument and talking normally on the phone, she claimed that I was a bad friend. I am not sure how that is possible when I had not seen her in three months and the last time that I saw her I drove her to I-Hop and treated her. Every other time after that, she provided a reason...or rather excuse as to why she couldn't hang out. I know she had a job as well, so if she said she was working, I would never press the issue.
When I spoke to her over the phone, she had the audacity to sound bitter towards me and talk to me rudely. My voice never sounded angry, it was never raised....I honestly just am fustrated with her. I am not going to approach her until she contacts me. Especially now that college has started, she will act like she is the only one in the world who is going through hard courses and having a job at the same time. I never play the "My horse is bigger than your horse" game with her reguarding college and jobs, I just listen. But after knowing her through middle school, high school and now into college, hearing her complain about her life as if she is the only one who has problems is starting to bug me. Then when I try to explain to her that everyone has problems, she goes off on me. I don't get it...