Why did my best friend suddenly start being mean to me?

Anonymous
Her and I have been best friends for 11 years. She moved away 5 years ago, like halfway across the country. We see each other twice a year usually, and we used to text or Skype every day. Now that she goes to a really demanding school, though, she's really busy so we don't talk as much. It's been months since we've had a real conversation and I have been the only one to reach out and contact first. When we do text, I'll write something decent, but only get one word answers back even when I ask how she's doing, stuff like that. So, finally after her ignoring me for a while, I texted her, "Dude wtf are we even friends anymore or like no????" This is how the rest of the conversation went:
Why did my best friend suddenly start being mean to me?
In our entire friendship she's never said anything meant to hurt me like that. The VERY few other times that she's been mad at me, she just ignores me for a few days and then we're over it. This time she actually said something. So, my question is, why would she say something like that? She knows that I just missed her because I told her that I do (she never responded to it though). What is going on with her?
Why did my best friend suddenly start being mean to me?
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