Longed to be a good little boy (5)
I believe the answer is:
pined
'longed' is the definition.
('pine' can be a synonym of 'long')
'a good little boy' is the wordplay.
I cannot really understand how this works, but
'good' could be 'pi' (old-fashioned term for pious) and 'pi' is located in the answer.
'boy' could be 'ned' and 'ned' is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
'to be' is the link.
Can you help me to learn more?
(Other definitions for pined that I've seen before include "Longed; wasted (away)" , "Languished, yearned" , "Starved" , "Became ill with longing" .)