sweetheart
n
1 (dated 旧) one of a pair of lovers 恋人; 情人
They were childhood sweethearts. 他们原是青梅竹马的恋人.
Mary has a sweetheart. 玛丽有个心上人.
2 (used esp as a loving form of address, eg to a wife, husband, child, etc 尤用作爱称, 如称呼妻子、 丈 夫、 孩子等).
Yes, I'm sorry about that. I think we just had a misunderstanding about the plan, but I was very disappointed not to be going out. So I got angry and started shouting at you.