Think incessantly, turning over actresses' bombshell revelation (6)
I believe the answer is:
obsess
'think incessantly' is the definition.
(eg obsessing about a person)
'turning over actresses' bombshell revelation' is the wordplay.
'turning over' says the letters should be written in reverse.
'revelation' indicates a hidden word (the answer is revealed within the clue).
'ssesbo' is hidden within 'actresses bombshell'.
'ssesbo' written backwards gives 'OBSESS'.
(Other definitions for obsess that I've seen before include "Persistently preoccupy" , "Bosses (anag.)" , "Think only" , "Preoccupy completely" , "Prey on" .)