When a girl suddenly stops talking to you?

I have been real close with this girl, liek bestfriends, we talk a lot in school, chat, and sms all the time. She tells me her secrets and problems and I tel her mine, I don't know if she likes me or not (because people keep on telling me that she does) i dont really know if I do, but one day she just stopped talking to me (after I left the country for a vacation). I don't know whats goin on. What does this mean?