We go through our whole life developing friendships. They can start with your family and then branch out over time. Some are life long, while others can come and go.
I recall my father telling me while in my teens that if you even have one or two true friends in your life time you can consider yourself lucky. How true this statement is while we grow older and see who truly relate to and stay in communication with.
The truth be told, we can tell who is a true friend especially during good and bad times. Hold onto those core friendships as they are rare and special. They will last a life time.