A good relationship wasted? (5)
I believe the answer is:
gaunt
'wasted?' is the definition.
('gaunt' can be a synonym of 'wasted')
'a good relationship' is the wordplay.
'a good' becomes 'g' (abbreviation).
'relationship' becomes 'aunt' (I am not sure about this - if you are sure you should believe this answer much more).
'g'+'aunt'='GAUNT'
Can you help me to learn more?
(Other definitions for gaunt that I've seen before include "place associated with Edward III's son" , "Thin or emaciated" , "forlorn" , "Hence John" , "Very slight" .)