There is a reason web sites find it difficult to define social relationships. On Facebook you need to be a former co-worker, lover, whatever to categorize someone.
But real life relationships don’t fit into tidy little boxes.
Currently I have a friend that is also a mentor, who is also a consultant working for me (through my client), and this friend is also a client of mine. All at the same time.
Define that relationship on the “social graph”.
Social networking is hard.