Regret the incompleteness of true love (3)
I believe the answer is:
rue
'regret the incompleteness' is the definition.
'rue' can be an answer for 'regret' (to rue something is to regret it). I am not certain of the 'the incompleteness' bit.
'of true love' is the wordplay.
'of' says the answer is hidden in the clue.
'RUE' can be found hidden inside 'true love'.
Can you help me to learn more?
(Other definitions for rue that I've seen before include "Swann's way?" , "Bemoan" , "Regret the bitter herb" , "Repentant sort of shrub?" , "Nice way" .)