Do you hang out with your sister a lot in waking life? Sounds like you're feeling like the two of you are growing apart, like you think she might want to go off on her own and you don't like the idea, or you think she wont be able to survive if she does. I mean that's what I say without knowing any of you; seems pretty straight forward imagery though, how would you feel if all those things were happening in waking life, unlikely as it may seem?