Supporter of poor sons losing love, abandoned (7)
I believe the answer is:
sponsor
'supporter' is the definition.
(a sponsor is a financial supporter)
'poor sons losing love abandoned' is the wordplay.
'losing' is a deletion indicator.
'love' becomes 'o' (love means zero in tennis).
'abandoned' is an anagram indicator (the original order is abandoned).
'poor'+'sons'='poorsons'
'poorsons' with 'o' taken out is 'porsons'.
'porsons' is an anagram of 'SPONSOR'.
'of' acts as a link.
(Other definitions for sponsor that I've seen before include "Financial backer" , "One funding an event" , "Supporter or champion" , "Promoter, godparent" , "One paying to support" .)