Soon desert old lover (9)
I believe the answer is:
inamorato
'lover' is the definition.
(I've seen this before)
'soon desert old' is the wordplay.
'soon' becomes 'inamo' (in a mo).
'desert' becomes 'rat' (ratting is a kind of deserting).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'inamo'+'rat'+'o'='INAMORATO'
(Other definitions for inamorato that I've seen before include "Italian lover" , "I Love A Lassie" , "Male lover" , "One who's fond of" , "Man loved" .)