A love letter disposed to show forbearance (8)
I believe the answer is:
'show forbearance' is the definition.
(I've seen this before)
'a love letter disposed' is the wordplay.
'love' becomes 'o' (love means zero in tennis).
'disposed' indicates anagramming the letters.
'aoletter' with letters rearranged gives 'TOLERATE'.
'to' acts as a link.
(Other definitions for tolerate that I've seen before include "Allow" , "Put up with, permit without protest" , "Put up with, bear" , "Put up with something or somebody" , "Endure, put up with" .)