Little upset with sweetheart girlfriend? (4)
I believe the answer is:
date
'girlfriend?' is the definition.
(date can mean someone you are dating)
'little upset with sweetheart' is the wordplay.
'little' becomes 'tad' (both can mean a small amount).
'upset' is a reversal indicator.
'with' is a charade indicator (letters next to each other).
'sweetheart' becomes 'e' (the heart/centre of 'sweet').
'tad' in reverse letter order is 'dat'.
'dat'+'e'='DATE'
(Other definitions for date that I've seen before include "one's arranged to meet" , "For example, sell by" , "escort" , "Oval fruit" , "Romantic assignation" .)