Losing friends (angry rant. I apologize ahead of time).

I can't really think of any old friends who I stopped liking. Plenty of them have stopped liking me, though. I don't really know how it happens, but I think somewhere along the line they realize how boring I actually am and find someone who they like better.
i mean, I can remember all of the times it happened through the years with almost all of my "best friends". And I hate it! I just want to complain about it, so don't keep reading if you don't want to know.
I know it's the natural course of relationships to move on and make new friends and whatever. What bothers me is how easily I'm replaced. I hate being the back burner friend, but so often I'm the one people put off, knowing that I'm lame enough to always be available and want to pick up where we left off. But eventually I think they realize that life is going fine without me in the picture, so... on to new and better things.
Before you tell me I'm imagining, let me just lay out some scenarios. True stories from my life.
1) Third Grade: Best friend is in a different class and actually asks me if it's OK with me if she plays with other kids during recess.
2) forth grade: They made a new class mid-year by taking out kids from every class. The only kids from my class that I was friends with were moved, and they really never talked to me again.
3) Seventh grade: My whole group of friends close off the lunch table to me and stop inviting me to do things with them. True story.
4) Eighth grade. Friend who has been close friend and family friend since third grade decides to be popular, thus leaving me in the shadows and completely ignoring me thereafter.
5) Ninth grade: the only friends I had from middle school both wanted to seek their fame in high school. After hanging out a little first semester, they made better friends and never talked to me again.
6) Ninth grade: I left the church, and the one guy I ever really liked and probably would have dated eventually called me up to argue about it. Unresolved argument. He never called again.
7) First year of college: Best friend, very best friend I ever had, has some biff with me that she never shared. I'm kind of dense and didn't realize it, and kept trying to call her and chat online, and i think she actually started hating me all the while. She came out of the closet and didn't tell me, and I guess i did something terribly wrong that year because I think she truly hates me. It breaks my heart because I really loved her.

Those are real examples, completely unexaggurated. I don't know what the "thing" is about me. I can't tell if it's an ideal problem, because a lot of clsoe friends I had shared the same values and then moved away from them. What pisses me off about that the most is that I WASN"T THE ONE WHO CHANGED yet they put words in my nmouth and thoughts in my head and decide what I think about them, personally, just because I might not agree about some new idea they've adopted. Yes, I'm opinionated. No, I'm not a hater.

Or maybe the problem is what I've always suspected. That people find me dull on almost every level. Or that no one gets me. And really hardly anyone really does, but I'm not a picky friend. I just like to be called once in a while or sent an email, or invited to do something. I don't mind being the one to initiate even, but after about six tries, I get discouraged and just can't get myself to be rejected again.

So if you ever wanted to know what my deepest source of insecurity is, that's it.