GBF-Gay best friend. A Gay best friend is a male best friend to a woman. A Gay best friends doesn't necessarily have to be gay. It can just be a boy/man that you could never be lovers with but you still do everything with. You can have more than one GBF any boy/man you can trust to go shopping with, share feelings, etc.
Girl: "Omg Will I love you, but not like that."
Will: "That's right because I'm you GBF