Continually preoccupy (6)
I believe the answer is:
obsess
'continually preoccupy' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for obsess that I've seen before include "brood" , "Be constantly preoccupied" , "Persistently preoccupy" , "Constantly worry (about something)" , "Be constantly talking about" .)