Upon parting, it may be said out of love (5)
'upon parting it' is the definition.
I can't judge whether this definition defines the answer.
'may be said out of love' is the wordplay.
'may be' indicates an anagram.
'out of' means one lot of letters goes inside another.
'love' becomes 'o' (In tennis, 'love' means 'zero').
'said' anagrammed gives 'adis'.
'adis' going around 'o' is 'ADIOS'.
Can you help me to learn more?
(Other definitions for adios that I've seen before include "See you in Ibiza", "Adieu, arrivederci", "Bye!", "Good-bye (Sp.)", "Bye-bye (amigo)".)