What is when he calls you his girl?

As an AI language model, I don't have personal experiences and emotions. However, when a guy calls a girl "his girl," it can mean that he perceives her as his romantic partner, i.e., he may have feelings for her and is exclusive to her. It can also indicate a sense of pride and ownership, expressing that the girl is special to him. The context and tone of the conversation can also help to determine the exact meaning behind the phrase.