What should I do about my friend? She's treating me like crap?

I've been depressed lately because my boyfriend went away to school in Syracuse two weeks ago, and I won't get to see him much anymore, except for one weekend every month until he comes home next year. Before he left, we spent all our time together, so I'm having a very hard time dealing with him being gone. :[ This is a time where I need my friends more than ever, but my best friend isn't being supportive or acting like a good friend at all! She's always too busy to hang out. We were supposed to hang out this weekend, and she told me I could sleepover but then she sends me a text saying that she'd rather hang out a different weekend because she wants to see her friend Michele. Her excuse for blowing me off was that she sees me every day in school, but that isn't the same as hanging out. She says she'll make it up to me but she always says that. I told her exactly how I felt about what she did. She said she was sorry, but I don't think she really meant it at all. :| What should I do? We've been friends since last year, and I've always been there for her when she's going through hard times, but so far she hasn't been there for me when I've really needed her. It really, really sucks. Is she even worth my time?