Forgive old flame being almost exhausted (6)
I believe the answer is:
exempt
'forgive' is the definition.
(I know that forgive is a more specific form of the action exempt)
'old flame being almost exhausted' is the wordplay.
'old flame' becomes 'ex' (an ex-partner).
'being almost exhausted' becomes 'empt' (I can't justify this - if you can you should give a lot more credence to this answer).
'ex'+'empt'='EXEMPT'
Can you help me to learn more?
(Other definitions for exempt that I've seen before include "Excused - let off" , "may mean the taxman may ignore some charge" , "Free from liability. excused" , "Not liable, as others may be" , "free from tax, say" .)