I consider myself to be my best friend.  That isn't meant to sound ego-centric or narcissistic.  I don't always do what is in my own best interests.  But no one else consistently and totally has my best interests at heart at all times.

If I set aside the conventions of the material world then my higher consciousness and everyone elses higher consciousness and all the angels and the metaphysical components that constitute the Divine Oneness of Being are co-equally my best friend.  Because there is no separation spiritually I do not have a multitude of metaphysical best friends but only one - call it whatever you will.

There are many friends in the material world, who provide me with different and overlapping things.  There are a few who know me very well and fairly clearly and can function as "best friend".  I could narrow it down to one person that is currently most clearly fulfilling that role but all my friends have a significant part to play.

my partner is my best friend and my only friend.

Myself

how you can you be your best friend?

When a person says, "I am my own best friend", I think, sometimes, they are really (either consciously or subconsciously) affirming responsibility for the choices they are making in nurturing their self and their desired direction in life.
One of the things I regret in life is not nurturing friendships I made when I was younger.  As a result I have no history with anyone I now know (except for my family so, it's lucky for me that they are so very loving and special...I always jokingly say to people, "I hope I get the same ones in the next life"  lolol!!).  As for friends I had through my later twenties, they were probably not really my friends and so, when I cleaned up my substance abuse in 2000, I severed all of those social ties.  I have yet to make new friends but I have opted out of life in some ways till now and I'm sure that is why.  When I opt back in, lol, I know this will follow.
Did I introduce myself?  My middle name is "Procrastination" lmao
Love to you
Peta