Some friendships do last 'forever' and I don't think anyone enters any friendship thinking to themselves, "oh, I'm only going to tolerate this mofo for a year and then I'm on to the next one". When friendships fizzle, both parties go through their moments of wondering what went wrong. Some people blame the other person 100% for the loss, others blame themselves. Then there are those who take the "reason, season" approach; they appreciate the time they did have and easily move on and away from said friend to go experience friendship with someone else.
From what I have observed, the friendships that hurt the most when you lose them are those that were actually built on what you believed to be a sturdy foundation because you'd been friends for SO long. There is this misconception that just because you are close enough to label one another "best friend" that you ALWAYS have to be in that persons life. You don't. Things fall apart sometimes and close friends can become enemies.
I'm currently seeing this happen with one of my friends. They've been friends with someone for over 20 years but they cannot even mention this persons name without a tinge of disgust in their voice. I totally understand the reasoning behind it but if I had to say which one was wrong, I'd say both are. One of the individuals has decided to move on and not discuss any of their feelings about their friend, WITH their friend. The other party involved chooses to express themselves through status messages, tweets, and pretending their other friendships are so much more important. Both people are just hurting each other even more; which makes their friendship deteriorate further.
For some, it becomes a blow to their pride to admit when they're wrong, jealous, hurt, or just don't like how they're being treated. Women tend to be able to do this easier but most men...they don't want to be looked at as acting like a chick so they'll let their friendship die. All in an effort to preserve an ego that probably caused their friendship to start crumbling in the first place.
I have been here before and I don't desire to go back. No matter how irritating it might be to someone, I will let them know when I have a problem. I don't feel like the demise of a friendship should come as a shock to anyone. Respect that person you heralded as a friend to let them know what's going on from your point of view. It does matter. If you were both in it to win it at some point, the least you can do is let that be known. After you let so much time pass, pretending not to care, it turns EXACTLY into you NOT caring. You become indifferent and that persons feelings are no longer even important to you...when "just a week ago" you would have defended them.
Long, meaningful relationships are worth attempting to save. The nature of your friendship might change but you don't have to "lose" a friend due to differences and misunderstandings; that's what communication is for. So, if you gave a damn about this person "just a week ago", let them know. Real friends are able to get pass bumps in the road. If you can't manage to do that, then maybe you weren't that good of friends to begin with...