a boyfriend or girlfriend

She eventually married her childhood sweetheart. 她最后嫁给了她儿时的心上人。

used for talking to a person that you love, especially a child or person you have a romantic relationship with

[ as form of address ] "Happy birthday, sweetheart," he said. “生日快乐，亲爱的。”他说道。

a kind and generous person

"Oh, you're a sweetheart," she said, when I brought her breakfast in bed. 当我把早餐送到她床上的时候，她说：“哦，你真好。”