Loved nothing about, in sum (6)
I believe the answer is:
adored
'loved' is the definition.
(adoring is a kind of loving)
'nothing about in sum' is the wordplay.
'nothing' becomes 'o' (looks like zero - 0).
'about' becomes 're' (regarding**).
'in' is an insertion indicator.
'sum' becomes 'add' ('add' can be a synonym of 'sum').
'o'+'re'='ore'
'ore' going within 'add' is 'ADORED'.
(Other definitions for adored that I've seen before include "Doted on" , "Loved intensely" , "Loved dearly" , "Idolised" , "having lover" .)