Why are my friends being mean

I just finished your 11 and all my friends have decided to drop me with no reason and they weren’t even tell me why they’ve just stopped talking to me completely

I’ve not done anything wrong, but I believe I’ve been nothing but nice there was just suddenly a switch up with them or they just started being quite horrible to me the past couple weeks

For example, on Friday we had revision and I had saved us a table but as time went on people came and sat in the table because they have finished an exam. And they were decided although there were still seats open next to me to sit somewhere else and only one of my friends was left and there was only two seats left both the next to me and she chose to pick up the booklet that was next to me and go sit in the back where I by herself next to no one and as she walked past me smiled at my two other friends and they all were laughing. 

I couldn’t handle that sappy and began to crying was sent out the revision lesson because how else was I supposed to react? You reacted as if you were gonna sit next to me and then picks up the book next to me and started laughing at the fact that you wouldn’t sit with me and I haven’t done anything and that’s what I’m so confused about and nothing but nice to them. I compliment them and ask them how their day is so I don’t understand why they’re all just being so mean.

But one of them then I swear it’s only in the group only one of them is really really nice to me all the time and she’s amazing but because she spends with them I don’t think I’m going to be invited to hang out with them this summer, so I’m practically over for three months.