Love shown by husband leaving this regretful lady (4)
I believe the answer is:
otis
'regretful lady' is the definition.
(Miss Otis Regrets is a song by Cole Porter)
'love shown by husband leaving this' is the wordplay.
'love' becomes 'o' (love means zero in tennis).
'shown by' is a charade indicator (letters next to each other).
'husband' becomes 'h'.
'leaving' is a deletion indicator.
'this' with 'h' taken away is 'tis'.
'o'+'tis'='OTIS'
(Other definitions for otis that I've seen before include "Regretful miss" , "regretful lady" , "lift company" , "-- Redding, US singer" , "Miss -- Regrets, Cole Porter song" .)