Separated father comes back with gallery contents (5)
I believe the answer is:
apart
'separated' is the definition.
(synonyms)
'father comes back with gallery contents' is the wordplay.
'father' becomes 'pa' (pa can mean dad or father).
'comes back' is a reversal indicator.
'with' means one lot of letters go next to another.
'gallery contents' becomes 'art' (I've seen this in another clue).
'pa' written backwards gives 'ap'.
'ap'+'art'='APART'
(Other definitions for apart that I've seen before include "Isolated" , "In private" , "Separated physically" , "Separated; to one side" , "No longer living together" .)