A sweetheart possibly glowing (6)
I believe the answer is:
aflame
'glowing' is the definition.
(thesaurus)
'a sweetheart' is the wordplay.
'sweetheart' becomes 'flame' (I've seen this in another clue).
'a'+'flame'='AFLAME'
'possibly' is the link.
(Other definitions for aflame that I've seen before include "Ardent" , "very hot" , "fired up?" , "Ablaze" , "Ma, flea could be burning" .)