Type 3: Perfect Friendship
Aristotle says:
"Only the friendship of those who are good, and similar in their goodness, is perfect. For these people each alike wish good for the other....and it is those who desire the good of friends for the friends sake that are most truly friends because each loves the other for what he is and not for any other reason"
So these friendships last as long as both remain good.
The reason why good people are friends with other good people? They both express the same good behaviors each of them admires.
Generally, once a person becomes good they remain that way; hence, if two good people meet, it's expected they'll form a lifelong friendship and it's unlikely that such a friendship would ever dissolve like the capricious friendships of pleasure and utility.
The catch is that these friendships are so rare, some truly good people may never experience it in a lifetime as Cicero once mentioned.
How many of these friends do you have? How many of your friends are truly happy when good things happen to you? Conversely, you should ask yourself if you're sincerely happy when good things happen to your friends.