Disclaimer: I have fantastic friends and they know who they are, even if I don't see them or talk to them as much as I would like to, because life. This isn't about them. In fact, it's not really about anyone in particular.
Over the years I've had friends who just haven't stayed the distance. In some cases there were clear reasons why we 'broke up', in others we just drifted apart, no real issue that caused the demise, just neither of us made any effort anymore, and there's no hard feelings. Eventually though, there's unfriending on Facebook and just no more contact. Although if I saw them i the street I'd probably say hello and stop for a chat.
There's been a couple of people who have just plain and simple stopped returning my messages. For no reason that I know of. But having said that. I'm also guilty of 'phasing people out', and I have my own reasons for that, so I'm guessing they do as well. That's life!
I read a thing once (and forgive me if I get this wrong, I can't be bothered googling it as I tap this out on my phone when I really should be asleep) anyyyyyyway, the thing said that friends don't have to be forever to mean something. The universe provides us with the right person at the right time. To teach us something, it to help us deal with something, or even just to have a damn good time. They do their 'job' and are gone. We may mourn it for a bit, or we might not even notice. This makes sense to me.
I've got my own theory about friendship. Think about your really close friends, the ones you've had for ages. I bet they have other close friends as well, hell, their close friends could even be YOUR close friends. That's because good people surround themselves with other good people. They've weeded out the crap over the years.
We don't have to be BFF's with everyone we come across. Yes, we need to be respectful and polite, but we don't need to start threading friendship bracelets straight away. I barely have enough time for the friends I do have, let alone new ones. As a friend of mine likes to say 'I'm not hiring right now!' Having said that, you can always make room for the perfect candidate, can't you?
And finally, something I have noticed over my time on this planet is that women who don't have at least one close girlfriend they've had for years turn out to be people I should NOT have trusted. Always. Without exception. I reckon there's a reason for that. I'm going to try and learn to trust my gut more. In the past I have given too many people the benefit of the doubt, and I'm the one that ends up suffering. No more!