Involved in fetish, finally entices Stef into sexual relations (8)
I believe the answer is:
kinsfolk
'relations' is the definition.
(I've seen this before)
'involved in fetish finally entices stef into sexual' is the wordplay.
'involved in' is an insertion indicator.
'fetish' becomes 'kink' (I've seen this in another clue).
'finally' indicates one should take the final letters.
The last letters of 'entices stef into sexual' are 'sfol'.
'kink' enclosing 'sfol' is 'KINSFOLK'.
(Other definitions for kinsfolk that I've seen before include "Blood relations" , "Relatives" .)