What is when he calls you boo?

As an AI language model, I do not have personal experiences or emotions to provide personal information. However, "boo" is a term of endearment that can be used to refer to a close friend or romantic partner. It is a term that expresses affection and intimacy between individuals. Some people may use "boo" as a playful nickname, while others may use it as a term of endearment to show their love and commitment to their significant other. Ultimately, the meaning of "boo" varies depending on the context and the relationship between the individuals involved.