I don't know how to react

I'm in 8th grade, and I am about to graduate from Middle School in about 3 weeks or so. I've been planning to go on trips and hangouts with my friends since many of them are leaving. I was just talking to my friends that are twins, and they are leaving soon after graduation, and they have a lot of plans with others. I found out that 6 of my closest friends, including them are going to Disney 2 days after graduation, and they kept that away from me for over 2 months and they were planning on not inviting me anyways. I really don't know what to say and how to react. I feel like I just lost all faith in everyone, because I thought I was close with them. I feel so down because those really are my only true close friends and I feel like I just lost them all. I keep imagining them having so much fun and me at home going through their snapchats and feeling all depressed. I don't know what to do. Someone please help me.

Do you live near Disney? I ask because if not, this could be more about the group of parents involved. I have a friend and of course through fb, noticed this group of them are planning a sweet vacation next year, but they needed to book now to get some fabulous rates. Not that it's any of my business, but taking a guess about this Disney vacation and trying to explain how though you feel left out, right now, it's about their families.
Certainly you'll have other plans forming for this summer?

Well I don't live near Disney, but I live in a safe community where kids go wherever especially to amusement parks without parents. And they told me that they left me out so that there is an even number. It's my last chance to hangout with 3 of my closest friends but I guess I won't even have that chance.

There's simply not enough information to know why they excluded you, but I can only imagine how horrible you feel.