Financial backer admitting love for architect (7)
I believe the answer is:
founder
'architect' is the definition.
(thesaurus)
'financial backer admitting love' is the wordplay.
'financial backer' becomes 'funder' (someone providing funding).
'admitting' means one lot of letters goes inside another.
'love' becomes 'o' (love means zero in tennis).
'funder' placed around 'o' is 'FOUNDER'.
'for' acts as a link.
(Other definitions for founder that I've seen before include "One sets up firm" , "(Of ship) fill with water and sink" , "Sink like originator?" , "Institution's former" , "collapse" .)