I also recently went through something like this. My bestie was also self centered but this helps you in the end because you can now spend your time on someone who cares.
Cassy, I understand what you're going through. Well, the general aspect, with the supposed best friend not caring about you. I too went through something like that, where I lost my best friend and the messed up part about it was that it hurt me a thousand times more than it hurt her.
But maybe, have you ever thought that something, whatever you went through, happened to show you that she wasn't as good a friend as you thought of her to be? Just my opinion.
I think, you shouldn't bum yourself so much about it. Things happen in life, and most things happen for a reason. Take this as an eye opener. Just because you lost one person, doesn't mean that they're all gone.
Hope things work out! Venting always works out, but never act on anger—the results come back to get you in the end.