Learner finished as sweetheart (5)
I believe the answer is:
lover
'sweetheart' is the definition.
(sweetheart can mean a lover)
'learner finished' is the wordplay.
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'finished' becomes 'over' (over can mean finished or ended).
'l'+'over'='LOVER'
'as' acts as a link.
(Other definitions for lover that I've seen before include "Opposite of hateful type" , "toy boy" , "I could be fickle" , "Romantic partner" , "Boyfriend" .)