suprafriend
This is the name and designation of the friend who you have been friends with longer than any other. Suprafriend is the title awarded to the longest standing friendship. Suprafriend is the person in your life who you have known and been friends the most number of years. (instead of saying my "oldest" friend, which sounds like the friend is of old age)
I am going on vacation with my sister, a work friend, my best friend, and my suprafriend.