Friendship

Like I said briefly in my last post, I went to see Noah with a friend. Without mentioning any names, I'd like to discuss my relationship with this friend and with others.
I've known this girl since I was three. Her aunt used to babysit me and my siblings, so I used to hang out with her and her siblings a lot, since both of my parents worked on weekends. We used to watch movies like Sharkboy and Lavagirl in 3-D, or eat chicken nugget dinosaurs and macaroni. I didn't know why at the time, and I doubt I even noticed, but I stopped seeing her when her aunt stopped babysitting me and she went to a different school. However, in second grade, she transferred, and we were in the same class.
We were best friends until sixth grade. I slept over her house practically every other weekend, and we watched movies like Jeepers Creepers and The Haunting in Connecticut while eating pizza. But, in December of sixth grade, she had to move again, this time to another school district. For about a year, we maintained this friendship, and I slept over even more often. I even went to Ocean City for a week with her family.
In the eighth grade, we stopped, and I don't know why. It always seemed like every time we asked the other to hang out, the other one was busy. I tried inviting her to birthday parties, but since I joined STAC, it was kind of awkward to have just one person who didn't know what was going on. I didn't even bother to invite her to my fifteenth birthday, but I asked her to hang out the next weekend. Going to see Noah was the first time I saw her since then.
I have felt extremely guilty for a long time for a number of reasons. This isn't the only friendship that I've let go to waste, and I don't know if that is a flaw in my character or if it really is natural to grow apart from some people. I feel like once I joined STAC, I met these great new people and neglected my old friends. To be fair, some of them weren't that great, and dropping them was more or less intentional, but there were some people who didn't deserve it. I love the friends I've made in STAC, but I'm terrified that when they graduate I won't have anybody. I won't have friends to go to prom or graduation with. Even when I take midterms or finals, I have to scrounge around to find people to hang out with, and even they are casual acquaintances at best. Lately, I've been hearing about all of these Sweet 16's, and I haven't been invited to any. This isn't the classic nerd exclusion, either, because I know that there are people that like me, but it might be my fault that I don't put enough effort into friendships. That's why they either slip away or fail to form, and why the most stable friendships I have were formed by my sister.