Sensitive about being Cupid (4)
I believe the answer is:
eros
'cupid' is the definition.
(thesaurus)
'sensitive about' is the wordplay.
'sensitive' becomes 'sore' ('sore' can be a synonym of 'sensitive').
'about' says the letters should be written in reverse.
'sore' reversed gives 'EROS'.
'being' acts as a link.
(Other definitions for eros that I've seen before include "divinity" , "asteroid four hundred and thirty three" , "God of love - example of 1 down" , "Piccadilly 14 ac statue" , "Cupid, son of Aphrodite" .)