Student finished with sweetheart (5)
I believe the answer is:
lover
'sweetheart' is the definition.
(sweetheart can mean a lover)
'student finished' is the wordplay.
'student' becomes 'l' (as in L-plates for learner drivers).
'finished' becomes 'over' (over can mean finished or ended).
'l'+'over'='LOVER'
'with' acts as a link.
(Other definitions for lover that I've seen before include "One has favourite" , "finished litre first" , "Paramour" , "admirer" , "Juliet, for example" .)