Endless indulgence? Of course, sweetheart! (8)
I believe the answer is:
treasure
'sweetheart' is the definition.
(both are terms of endearment)
'endless indulgence? of course' is the wordplay.
'endless' means to remove the last letter.
'indulgence?' becomes 'treat' (to indulge yourself is to treat yourself).
'of course' becomes 'sure' (I've seen this before).
'treat' with its last letter taken away is 'trea'.
'trea'+'sure'='TREASURE'
(Other definitions for treasure that I've seen before include "Gold on this island" , "Accumulated wealth, could be buried" , "Valued possession, buried perhaps" , "... Island (R.L.Stevenson)" , "Set great store by" .)