You can make a friendship last by building it on a lasting foundation. The foundation must be built on trust reliability and caring. If it has these key ingredients then all one must do is maintain them to have a healthy and long friendship.
The friendship will last as long as you stay in touch and contact with the person. You do not even have to go out and do activities with the person; you merely need to keep that connection via talking, if not visiting, so that you are still in touch with each other.