Lose hope when changing diapers (7)
I believe the answer is:
despair
'lose hope' is the definition.
(synonyms)
'changing diapers' is the wordplay.
'changing' indicates anagramming the letters.
'diapers' with letters rearranged gives 'DESPAIR'.
'when' acts as a link.
(Other definitions for despair that I've seen before include "Misery" , "Resignation" , "Be without hope" , "The feeling that nothing will turn out well" , "Despondency" .)