If friends disappoint you over and over, that's in large part your own fault. Once someone has shown a tendency to be self-centered, you need to recognize that and take care of yourself; people aren't going to change simply because you want them to.
A man cannot speak to his son, but as a father; to his wife, but as a husband; to his enemy, but upon terms: whereas a friend may speak, as the case requires, and not as it sorteth with the person.
If two friends ask you to judge a dispute, don't accept, because you will lose one friend; on the other hand, if two strangers come with the same request, accept because you will gain one friend.
When you part from your friend, you grieve not; For that which you love most in him may be clearer in his absence, as the mountain to the climber is clearer from the plain.