Does anybody know this idiom? I am not sure if the word truly has an "s" or not. The meaning I suppose: You can have many friends but you can one real friend.
I've not heard it, but if I were to coin it, I would say, "There are friends, and there is a friend."
Another possibility is: 'There are friends, and then there are friends.' which means there are people we casually call friends, and then there are the very special people we can count on to be our true friends (in times of need).