since your girlfriend is in dream it is related to her or your position towards he. Could mean something is worrying you and maybe you need more confidence in yourself in that relationship and be more assertive. Could be sexual aspect that you feel insecure about something too. If this is the case don't worry to much about failure, cause if it is meant to be it will go just fine.
Ask yourself what your feeling is in this relationship. If you have no sincere feeling for that girl it could mean you better end it. Could also be the otherway around...