sweetheart

sweet|heart /sw'iːthɑːrt/ (sweethearts)
1 [N-VOC]
You call someone sweetheart if you are very fond of them.
Happy birthday, sweetheart.
= darling
2 [N-COUNT] usu supp N
Your sweetheart is your boyfriend or your girlfriend. (JOURNALISM or OLD-FASHIONED)
I married Shurla, my childhood sweetheart, in Liverpool.