Dear Alyssa,
It's fine to have more than one "best" friend, particularly since they live in different places. Instead of telling each one something like: "You're really my best friend" and then feeling disloyal to the one who's not there, tell each one how much you care about her and how special she is. As you get older, you will continue to make friends who become very special to you. They shouldn't be competing with each other, but each will have a unique place in your life.

Dear Alyssa,
It is OK to have more than one best friend. In fact, I have many best friends. I have different kinds of friends, like my best friends from camp, from my neighborhood, who play sports with me, etc. It is perfectly OK.