Growing up and moving on

So this week, I've been thinking a lot about friendships and how they change over time.  I know it happens, but I hate for it to happen.  Living in a house of 35 other girls, it's easy to become best friends with your roommate or the girl next door, however, what happens when you switch roommates or someone isn't around as often.  And is it the fault of both people or just one for a friendship to slowly fade.

It's hard to say.  I know I hate feeling like I'm losing a close friend.  And I feel as though, once I feel someone slipping away, I try really hard to make contact and get together with that person so we don't lose our friendship.  It normally works, and normally is just a case of both of us being too busy.  But what happens when the other person doesn't reciprocate any of the feelings you are having and doesn't even appear to want to try?  

From experience, it's hard.  It makes me feel really down and sad.  I'm the type of person who wants to be liked by everyone, to get along with everyone and stay connected to her close friends.  And I know that it becomes difficult as we go through college and get closer to graduating.  

But why does growing up mean that we have to move on and leave our old friends behind?

I remember a song I learned years ago in the Girl Scouts when I was a brownie that I think says it all.

Make new friends, 
but keep the old. 
One is silver, 
And the other gold.