My first question is: Is there anything that's changed in your world that would have people behave like that? Have you changed your attitudes or expectations recently? While it looks like everyone else is shunning you, it could be a reflection of things changing in your life that are much closer to home.
As far as your friends go though, what people have said are true. Life is a mystery and part of that is cycles of nature such as growth and death. Your friends growing apart from you could be from a number of reasons, none of which really matter because the reality of it is that they are just not as close as they once were. The pain you are feeling is not sourced from them not being close, it's coming from your own attachment to them. You are upset because you liked being close. Your whole friendship is built on being very close, so as they distance themselves the friendship breaks down. If you really loved your friends honestly, you could accept their distance, but still reach out to them with love. Right now all that is being heard is "Why are you leaving me?!? Whyyyyyy?"
Why they are distancing themselves doesn't matter at all. In fact it looks like a good time to take a good look at yourself and see what's really going on. Accept that your friends aren't as close as they used to be, accept that they might disappear permanently, and then still be for them in every way and send your love. And lastly: Stop making it all about you.