Dear old lover musing (9)
I believe the answer is:
expensive
'dear' is the definition.
('expensive' can be similar in meaning to 'dear')
'old lover musing' is the wordplay.
'old lover' becomes 'ex' (I've seen this in other clues).
'musing' becomes 'pensive' ('pensive' can be a synonym of 'musing').
'ex'+'pensive'='EXPENSIVE'
(Other definitions for expensive that I've seen before include "Charging a lot" , "Very costly or dear" , "not going for a song" , "Pricey" , "priceless" .)