Why would all the people I meet act like this?

I have anxiety. It's hard for me to make friends. I sat by myself for like the first one and a half semesters... I finally find a group of people that say I can sit by them. And recently I guess they've decided they're too cool or something and when I sat at their table on Friday, they all got up and left in sequence. You don't even know how bad that feels for me... I'm depressed as is. I was like about to start balling. But I didn't, I got nervous, sat there alone and drank 4-5 bottles of water until I got water intoxication and was like puking. This is why I can't enjoy school, everyone I meet wants something and when they get it, they leave. One time a girl asked me to Sadies, but then two days before the dance she messaged me on Facebook (Like she's too good to talk to me in person) telling me how she doesn't like me and she's going with her best friend now. I messaged her back saying how that was just GREAT, so she "gave" me permission to go alone... like I couldn't go if she didn't let me. I seriously don't even know why I'm still around. I obviously don't affect anyone, I'm just someone for people to screw with. Not sure where I'm sitting at lunch tomorrow, not too happy about it either.