I've had a similar sort of thing. I had this friend the summer holidays before last, who I hung out with a lot and confided in. Then, all of a sudden she didn't come to school. I asked one of our mutual friends where she was because we had plans in the next couple of days and I was told that she had gone to Sydney (five hours away) for an unexpected holiday. When I asked her about it over FB, she admitted that something had happened at her house, only describing it as "an accident" and saying that her Mum and Step-father were splitting up. She then said that she might be staying there for some time, possibly forever. About two months later she stopped replying to messages and I learnt that "the accident" somehow involved her little sister. She still talked to other people from our school occassionally, but would never reply to me. More than likely due to the fact I inadvertedly broke up her relationship with her boyfriend rather than a Witness protection program, though.