The sudden addition of a younger sister in the dream shows that there are very few people you can talk to in reality. You are eager to have a friend who speaks from the heart. You feel that some words can only be said to your relatives, but you feel that it is not appropriate to say them to your parents.
You have feelings for this unexpected girl in your dream, which means that you don't like the person who likes you, and the person you like doesn't like you either. In reality, it seems difficult for you to pursue the person you like. You have had several failed relationships.