As I say,it is essential. Without friend you can not share your feeling, friends give moral support and help in many situations. I have some very nice friends and they help in every-time. There are two different types of friends, close and very close so i think friends are very closed to you are quite essential.
I think is simple "Do not expect over from your friends ".
Yes, friendship is very essential in a relationship.A good friend can be your good partner or may be your good life partner.The reason behind it is that when you are friend of someone ,your friend knows your positive and negative sides.