Free former partner married on merit (9)
I believe the answer is:
exonerate
'free' is the definition.
(I've seen this before)
'former partner married on merit' is the wordplay.
'former partner' becomes 'ex' (an ex-partner).
'married' becomes 'one' (I've seen this in another clue).
'on' is a charade indicator (letters next to each other).
'merit' becomes 'rate' (synonyms).
'ex'+'one'+'rate'='EXONERATE'
(Other definitions for exonerate that I've seen before include "Excuse" , "let off the hook" , "Justify" , "Pronounce not guilty of a crime" , "Free from obligation, blame" .)