Obsessive observer (6)
I believe the answer is:
voyeur
'obsessive observer' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for voyeur that I've seen before include "One who spies on others for sexual gratification" , "One who watches" , "One views for titillation" , "A secret spectator or peeping Tom" , "One deriving pleasure from spying on others" .)