Funny how a person can lose a friend as simple as forgetting that you have a nice dress hung in the corner of your wardrobe. Well, I guess that is the biggest problem. It is 'hidden' from your sight. Lost any contact you have with that one friend who once relied on you for companionship, put their heads on your shoulder when they are in strings of emotional rally, or just to be with you because your are a fun person to be with. Witty and humuorous. Understanding and (once) loyal. Passionate and charming. When all these seemed to complete your life (or even world), why do you still lose a friend?
My bet is that people change. The life around you changes. Your perception of the meaning of friendship is no longer what you think it is 2 (don't matter the figure) years ago. your expectations change. When you're more successful than the other, gap matters. You will soon be jealous of him/her (you deny it, but you'll soon believe it's true), no more pillow talks, no more meaningful conversations but instead, you talk bad things behind their backs, discriminate their likings/passions/hobbies/work/successes with your cliques (new buds, who are at the moment, at same level/boat as you), etc. So, it is either party to blame, really. I learnt my lesson.
Take note and be prepared. Life is not always what you want it to be.