Things to do if you have no friends?

I am 16 I have never had any friends ever even in Elementary school. I have never been invited to parties or even to hang out with people. I am very nice and I always try to help people. I have even taken cles to help my schools special needs kids. I am very smart but I am not into sports. How can I make friends? Everytime I ask people to join them they say no or go away loser. So this year I ate in the library with the librarian. I just want to be normal and go out with friends and on dates and have a girlfriend. What's harder is my sister has friends she's had sleep overs she been able to be a kid. What's even more sad is that my 9th grade English teacher has been more of a friend to me than anyone else. He emails me several times a day because the kids he teaches hate him and he doesn't have friends either. I wanted to eat lunch with him but the school district said it was inappropriate and that students and teachers can't be friends. I say why couldn't I can't they see I am not like everyone else and I have a higher maturity level. As long as it's not ual and he's no longer teaching me why can't I? What am I supposed to do just sit and cry because nobody wants to be around me and eat alone? I think that's what my school wants me to do what do they know about not having friends. I think they basically want me to be alone and miserable because of what "could" happen. It's all an umption and nobody wants to be blamed. Plus kids in one of my cles teased me because one of my teachers gave me a gift and I got a hug and the cl didn't get anything.