First, I love the fact that you covered this topic. Probably long overdue. But before this becomes an issue, I have found that the main reasons people lose friends are:

1. Preconceived ideas as to what the friendship should be

2. Like in a marriage, some people take on friends thinking that they will make them a fan of or something like that and it doesn't happen, so they stop being friends.

True Story: My best friend was John all though high school. I went into the service and it was crickets. Reason, he didn't like people in the military. When I got out, I had a wife, our son, my brother and sister and all our belongings that needed to be moved.

John, like me is 6' 3" and in great health (at the time) I said, will you help us move. His reply: NO I don't help anyone move. Being young. We stop being friends.

Today, I'm much older and understand this one key point about friends. Accept them for who they are.