Bitterly disappointed (6)
I believe the answer is:
gutted
'bitterly disappointed' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for gutted that I've seen before include "Disappointed (sl.)" , "Destroyed by fire, or informally overcome by emotion" , "Destroyed internally, as building by fire" , "Bitterly disappointed (slang)" , "how fish is prepared" .)