But is he soon to betray love? (9)
I believe the answer is:
inamorato
'but is he' is the definition.
The definition suggests a singular noun which matches the answer.
'soon to betray love?' is the wordplay.
'soon' becomes 'in a mo' (in a mo).
'to betray' becomes 'rat' (to rat someone out is to betray them).
'love?' becomes 'o' (love means zero in tennis).
'inamo'+'rat'+'o'='INAMORATO'
Can you help me to learn more?
(Other definitions for inamorato that I've seen before include "One who's fond of" , "He loves" , "Italian lover" , "Beau" , "I Love A Lassie" .)