Mature to split with sweetheart? (4)
I believe the answer is:
ripe
'mature' is the definition.
('ripe' can be a synonym of 'mature')
'split with sweetheart?' is the wordplay.
'split' becomes 'rip' ('rip' can be a synonym of 'split'**).
'with' is a charade indicator (letters next to each other).
'sweetheart?' becomes 'e' (the heart/centre of 'sweet').
'rip'+'e'='RIPE'
'to' acts as a link.
(Other definitions for ripe that I've seen before include "Opportune" , "Fully grown, ready for eating" , "At fruition" , "Strong-smelling" , "Right" .)