Mr. SuN has suggested examples of friendships from Epics or History. Suggested example are from Epics only. May be that an example from history will be difficult. I also thought about history. No true examples could be seen. Certain examples, like two kings joining together as friends just to defeat a common enemy, could be seen. At the same time certain persons, who are thick friends could be seen around us in this society. Even there is not much.
Let us wait for the responses from others. In history itself, perhaps, certain kings or heads of States might had been there.