Longed to be a good boy (5)
I believe the answer is:
pined
'longed' is the definition.
('pine' can be a synonym of 'long')
'a good boy' is the wordplay.
'a good' becomes 'pi' (I've seen this in other clues).
'boy' becomes 'ned' (**).
'pi'+'ned'='PINED'
'to be' is the link.
(Other definitions for pined that I've seen before include "Became ill with longing" , "Longed; wasted (away)" , "Languished, yearned" , "Starved" .)