SO, my last "friend" just told me they didn't want to be friends anymore, so now I have nothing to do at school. Yah, I know that sounds stupid, just, the thing is that I am not a really social person, and I a lot of the people at my school don't like me, so, I need something to occupy me so I'm not just wandering around with nothing to do, because if i'm not doing something I fell really uncomfortable. Probably because everyone else has something to do. The library is rarely open so I can't go there, I can't hang out in any of my teachers' rooms because we aren't allowed inside until the bell rings. Also, I have nowhere to go for lunch now, and I was thinking about just sitting in the office or counselors' office and not eating, but that's not full proof, so I think I could use some suggestions. You can't suggest making more friends, because I can't do that. There aren't a lot of people in my grade and They all already have those "groups" that you can't just waltz into and be a part of. SO, yeah, that's pretty much it, i did my best to explain it, but if you don't get it I understand.

Is there a place where you can sit at and no one would bother you, or you wont feel uncomfortable.
Then, here some options, bring a game to play, use your phone, write a story, get a book, find a hobby.

"My last 'friend' just told me they didn't want to be friends anymore, so now I have nothing to do at school."

Not having friends doesn't mean there isn't anything to do. An extra book or two in your bag won't kill you. If electronics are allowed at your school, you could also bring a phone or other device and play games or listen to music. As for where you can be, obviously I don't know how your school works, but if you have assigned classrooms, sit in your seat. It may sound like a stupid or strange thing to do, but people will get used to it. If there are no assigned classrooms or it gets locked, you can always find other places to go. I know someone who used to sit by the lockers the entire lunch period, listening to music and playing games on their phone.

I find talking with people younger than me helps. Maybe 1-2 grades younger is okay. I never really made friends with people from my grade cuz they already have 'groups' as you mentioned.