Roman's love for a domestic animal (4)
I believe the answer is:
cato
'roman's' is the definition.
(I've seen this before)
'love for a domestic animal' is the wordplay.
'love' becomes 'o' (love means zero in tennis).
'for' says to put letters next to each other (I've seen this in other clues).
'a domestic animal' becomes 'cat' (I've seen this before).
'o' put after 'cat' is 'CATO'.
(Other definitions for cato that I've seen before include "classical writer" , "Ancient Roman censor" , "Senator" , "Roman statesman" , "Marcus Porcius - , Roman politician, censor" .)