I think before you answer this you have to first determine what establishes a best friend?
Is it the person you’ve known the longest? Your Favorite?
To me your best friend can be anyone, a person you have known for a week or a person youve known for a lifetime. As long as the bond is their. Typically that means the latter.
In theory for most people a best friend is someone you should be able to tell anything to. Think about you life and its hidden details what are the things you cant tell people. I have them and so do you. Do go out and expose yourself to the world but instead find out why you cant and work on those issues instead. You’ll open up more to people while still protecting yourself. That in itself will create the strong bond that is needed to strengthen and build those irreplaceable friends.