A person I follow in the social networking world was talking about friendships. Everyone has a desire to be liked, appreciated and even loved. Humans are not meant to go through life alone. So many people are out there without someone to talk to or hang out with. Everyone has felt lonely at times in their lives.
Another take on friendship is that perhaps life-long friendships are not what they used to be. Maybe its more temporal.
Sometimes there are expiration dates on friendships. I have had friends come and go over the years. Not to sound cynical but there are some friendships that are there for the moment. In terms of your relationships with the opposite sex perhaps there are expiration dates there for a reason.
If you long for a old friend back in your life you need to examine your reasons for wanting that person back in your life. You need to ask yourself if you are emotionally ready for it. No need inviting stress or drama in your life unnecessarily.
Be good to your friends. They can be valuable assets in your life.