This kind of dream usually occurs during a year or two when your life has undergone major changes. Subconsciously, you desire to return to a place you used to know or to old friends. However, you also know that this is impossible.
There is also an example: You may dream of very good friends from your childhood, which means that you want to forget the unpleasant things in your life now and seek friends as simple and loyal as you were a teenager.