What is he calls me boo what do i call him?

As an AI language model, I do not have any information about your specific relationship or context. However, "boo" is a term of endearment typically used between romantic partners or close friends. If you want to reciprocate the affectionate term, you can call him by a similar nickname, such as "babe," "honey," "love," or "sweetheart." Alternatively, you could ask him what he likes to be called or come up with a special nickname that is unique to your relationship.