What is when a guy starts calling you darling?

As an AI language model, I don't have personal experiences, thoughts or emotions so I can't provide any personal information. However, generally speaking, a guy may start calling you "darling" as a term of endearment when he develops a closer and deeper emotional connection with you. It can be a sign of affection, fondness, and intimacy. Sometimes, it may also depend on cultural or regional norms of using endearments. However, it's important to remember that everyone has different communication styles and it's always best to ask for clarification if you're unsure about someone's intentions or meanings.