Lover's farewell number — entertaining end to concert (9)
I believe the answer is:
valentine
'lover's' is the definition.
(valentine is a kind of lover)
I cannot understand how the rest of the clue works.
(Other definitions for valentine that I've seen before include "Potential lover" , "Card to sweetheart" , "Message for February 14" , "Saint of sweethearts" , "Love card" .)