Having an affair; affectionately, if nothing else (4,4)
I believe the answer is:
with love
'else' is the definition.
Both the answer and definition are adverbs. Maybe there's an association between them I don't understand?
'having an affair affectionately if nothing' is the wordplay.
I cannot really see how this works, but
'having' could be 'with' (I've seen this before) and 'with' is present in the answer.
'nothing' could be 'love' (love means zero in tennis) and 'love' is located in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Another definition for with love that I've seen is " See 10".)