My favorite topic to discuss. I think, there is no other relationship that could even be compared to friendship.
Why ? Because your true friends will be with you all the times, from your childhood to your death, without any expectation from you. All the other relationship in this world has some sort of expectations.
And you can share everything with a true friend, which you cannot do with anyone else. Take your parents, or wife or children. There is certainly a boundary there, but a friendship has no boundary.
And most importantly, a friend can change your life as well. Good way or bad way depends on what kind of friend you have. But a Good friend can guide you for ever in your life and provide every support, when you need them. He will be with you to cry with you in your moments of break down, and he will be with you to celebrate in joy.
And last not but least, don't judge a friend by qualification or status or wealth. A friend is simply a friend. I have a very old good friend, who has been with me for almost 35 years, and I hope it will continue till either of us dies. Now my family also realizes the importance of the relationship and give us the space.
I hope, everyone finds such a good friend.