Unhappy when second entreaties faded outside (10)
I believe the answer is:
displeased
'unhappy' is the definition.
(thesaurus)
'second entreaties faded outside' is the wordplay.
'second' becomes 's' (common abbreviation).
'entreaties' becomes 'pleas' (plea is a kind of entreaty).
'faded' becomes 'died' (I've seen this before).
'outside' indicates putting letters inside.
's'+'pleas'='spleas'
'spleas' put within 'died' is 'DISPLEASED'.
'when' is the link.
(Other definitions for displeased that I've seen before include "Upset" , "Not happy" , "Angry" , "Furious" .)