Former partner, thoughtful and dear (9)
I believe the answer is:
expensive
'dear' is the definition.
('expensive' can be similar in meaning to 'dear')
'former partner thoughtful' is the wordplay.
'former partner' becomes 'ex'.
'thoughtful' becomes 'pensive' ('pensive' can be similar in meaning to 'thoughtful').
'ex'+'pensive'='EXPENSIVE'
'and' acts as a link.
(Other definitions for expensive that I've seen before include "High in price" , "Pricey" , "Highly-priced" , "priceless" , "Charging a lot" .)