Your partner will have a hard time seeing you for the individual that you are, because they'll be so busy superimposing onto you their own glorified image of the lover that they want you to be. This image comes from a connection that dates back to another lifetime; this person was enthralled with you, and you were like a hero to them. That sense of infatuation has carried through to this lifetime, and if you become romantically involved, they will place you up on that same pedestal -- whether you deserve the elevation or not.
And while it's nice to be adored, you'll quickly grow annoyed at rarely being seen or understood for who you truly are. Try not to respond to this annoyance, however, with unpredictable behavior or unreliability. That will only increase your partner's confusion as to who you are and what your intentions might be, and they will work all the harder to fit you into their preconceived image of you. A much better approach would be to be straightforward with them from the beginning about your feelings and intentions regarding the relationship. If this is little more than a casual encounter for you, let them know that, gently but clearly. Clearing up these issues from the start will help to avoid upset later, and will help to resolve the karma left over from that long-forgotten time and place. The best that can come of this will be that you help this person get in touch with their own need for independence, individuality and spontaneity.