Failure of young socialite star to seal deal finally (7)
I believe the answer is:
debacle
'failure' is the definition.
(I have seen 'Utter failure' mean 'debacle' so perhaps 'failure' could also mean 'debacle')
'young socialite star to seal deal finally' is the wordplay.
'young socialite' becomes 'deb' (I've seen this before).
'star' becomes 'ace' (synonyms).
'to seal' means one lot of letters goes inside another.
'finally' suggests the final letters.
The last letter of 'deal' is 'l'.
'ace' placed around 'l' is 'acle'.
'deb'+'acle'='DEBACLE'
'of' acts as a link.
(Other definitions for debacle that I've seen before include "Rout; disaster" , "Utter failure" , "Utter disaster" , "Great disaster" , "A sound defeat" .)