To spoil is glued in, sadly (7)
I believe the answer is:
indulge
'to spoil' is the definition.
(synonyms)
'glued in sadly' is the wordplay.
'sadly' indicates an anagram.
'glued'+'in'='gluedin'
'gluedin' is an anagram of 'INDULGE'.
'is' acts as a link.
(Other definitions for indulge that I've seen before include "take to the drink?" , "Pamper - eluding (anag)" , "Favour, gratify" , "Yield to the wishes of" , "Drink too much" .)