That isolation, and being left out of things, sometimes is a result of bullying (might have been in my case), but I think that it hurts more than actually being physically bullied. I know what you're talking about. I gave up on having friends when I was pretty young, and I don't think I ever really did learn how.

But here is something to try. Each day, make an effort to notice the times when your friends are there for you, and they show that they care. Keep a journal of those things (don't worry about the misses when they might walk with someone else or something - as you said, they have other friends too and that doesn't mean they aren't your friend anymore). Keep working on building your case for believing that your friends really do care about you. Maybe the ones you hung around with when you were younger weren't really good friends, but that says more about them than about you. Things are different now. And don't forget, we care about you here too.