On reflection, love story ending in wedding is sweet (6)
I believe the answer is:
gelato
'is sweet' is the definition.
(gelato is a type of dessert or sweet)
'on reflection love story ending in wedding' is the wordplay.
'on reflection' shows that the letters should be reversed in order.
'love' becomes 'o' (love means zero in tennis).
'story' becomes 'tale' (synonyms).
'ending in' suggests the final letters.
The last letter of 'wedding' is 'g'.
'o'+'tale'+'g'='otaleg'
'otaleg' backwards is 'GELATO'.
(Other definitions for gelato that I've seen before include "treat in Milan?" , "Frozen food" , "Italian-style ice cream" , "Italian ice cream" .)