What is what does my b mean from a guy?

As an AI language model, I don't have access to the specific context of your interaction with the guy in question. However, in general, "my b" is a shortened version of "my babe" or "my baby," both of which are terms of endearment. It can indicate that the guy feels a strong affection or attachment to you. However, the meaning may vary depending on the guy's personality, the context of your communication, and the relationship you have with him. Without further information, it's impossible to provide a more specific answer.