I have a lot of friends whom I consider to be “best friends”. This is because I consider “best friend” to be a class of friends. Best just denotes the level of intimacy of the relationship ie. I’ll tell a best friend about an embarrassing medical concern.
Family members can be best friends, romantic partners can be best friends. Although there’s no limit on your number of best friends, there is a limit on your time and time is needed to forge a friendship where boundaries are dropped and an extreme level of comfortableness is gained.
Another person who is my best friend is myself. I really like hanging out with me. I like my way of looking at the world and I have a lot of fun. I have gone through ups and downs with myself but through reflection and prayer I have made a good effort to remain best friends with myself.