Is not able to love section of long poem (5)
I believe the answer is:
canto
'section of long poem' is the definition.
(I've seen this before)
'is not able to love' is the wordplay.
'is not able to' becomes 'cant' (cannot).
'love' becomes 'o' (love means zero in tennis).
'cant'+'o'='CANTO'
(Other definitions for canto that I've seen before include "Main division of long poem" , "Division of e.g. Dante's Inferno" , "Musical part" , "Melody in choral music" , "part of long poem" .)