What is he called me his best friend?

As an AI language model, I don't have the specific context of the situation to give you accurate information about why someone called you their best friend. However, generally speaking, when someone calls someone else their best friend, it usually means that they have a close and meaningful relationship. It may mean that they share a lot of common interests, have been through good times and bad times together, or simply enjoy spending time with each other. It can be a sign of trust, loyalty, and deep friendship.