Your question is about your girlfriend. She calls you brother hai. What about you? I don't know how to call him affectionate, do I? There are two words after her name, Sisi Lee. So personally, I suggest you call him Yimei, so it should be smooth and affectionate. Personally, I think it's a good name. You can call two people, that is, you come and I go. Brothers and sisters will definitely come together sooner or later.
Then it sounds like a person. I hope you like the answer to your question and can adopt it.
Finally, I wish you health and happiness, and I wish you two can get along happily together.