Reject fiancée, essentially following incentive (5)
I believe the answer is:
spurn
'reject' is the definition.
(synonyms)
'fiancee essentially following incentive' is the wordplay.
'essentially' says to take the centre.
'following' is a charade indicator (letters next to each other).
'incentive' becomes 'spur' (an incentive spurs someone on).
The central letter of 'fiancee' is 'n'.
'n' put after 'spur' is 'SPURN'.
(Other definitions for spurn that I've seen before include "Refuse with contempt" , "Contemptuously dismiss" , "discard" , "turn away" , "Reject disdainfully" .)