Lose hope when changing diapers (7)
I believe the answer is:
despair
'lose hope' is the definition.
(synonyms)
'changing diapers' is the wordplay.
'changing' is an anagram indicator.
'diapers' anagrammed gives 'DESPAIR'.
'when' is the 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" .)