If you are already having doubts about this friend, it could be the reason for having this dream. I've found that if something bothers you or if you think about it enough it can come up in your dreams. If could be your subconscious trying to help you work through the issue.
If you feel the dream is prophetic, look for signs in your day to day life that could relate to the dream. Do you notice anything that could relate to your dream? Do you see any similarities?