Be preoccupied and worried following difficulty (6)
I believe the answer is:
fixate
'be preoccupied' is the definition.
(fixating on something is being preoccupied with it)
'worried following difficulty' is the wordplay.
'worried' becomes 'ate' (something worrying may eat someone up).
'following' is a charade indicator (letters next to each other).
'difficulty' becomes 'fix' (fix is a kind of difficulty).
'ate' put after 'fix' is 'FIXATE'.
'and' is the link.
(Other definitions for fixate that I've seen before include "Obsess (on something)" , "Become absorbed" .)