Pretend to follow former lover's demand (5)
I believe the answer is:
exact
'demand' is the definition.
(I know that exact is a more specific form of the action demand)
'pretend to follow former lover's' is the wordplay.
'pretend' becomes 'act' (I've seen this in other clues).
'to follow' is a charade indicator (letters next to each other).
'former lover' becomes 'ex' (an ex-lover).
'act' after 'ex' is 'EXACT'.
(Other definitions for exact that I've seen before include "Demand payment" , "Absolutely right" , "Not approximate; inflict (revenge) on someone" , "Completely accurate" , "Precisely accurate" .)