Backsliding secretary disheartened by job in support group (8)
I believe the answer is:
apostasy
'backsliding' is the definition.
(thesaurus)
'secretary disheartened by job in support group' is the wordplay.
'disheartened' means to remove the middle letters.
'by' is a charade indicator (letters next to each other).
'job' becomes 'post' (post is a kind of job).
'in' indicates putting letters inside.
'support group' becomes 'aa' (I've seen this in other clues).
'secretary' with its centre taken out is 'sy'.
'post' placed into 'aa' is 'aposta'.
'sy' put after 'aposta' is 'APOSTASY'.
(Other definitions for apostasy that I've seen before include "Abandonment of religious beliefs" , "Abandonment of one's religion" , "Renunciation of a religious or political belief" , "Abandonment of one's beliefs" , "Renunciation of one's beliefs or principles" .)