Developed thick skin about love, or just cold-hearted? (7)
I believe the answer is:
callous
'cold-hearted?' is the definition.
(thesaurus)
'developed thick skin about love' is the wordplay.
'developed thick skin' becomes 'callus' (thickened skin that has developed on the body).
'about' indicates putting letters inside.
'love' becomes 'o' (love means zero in tennis).
'callus' placed around 'o' is 'CALLOUS'.
'or just' acts as a link.
(Other definitions for callous that I've seen before include "Cruelly unfeeling" , "Insensitive, cruel" , "Cruel and unfeeling" , "Heartless" , "Emotionally hardened" .)