you need to confront him and be strait forward i know its a hard step to take but you can't keep beating yourself up over one guy that you have no idea how he feels. once he tells you then i promise it will get easier to deal with him and that girl in the hall don't keep you feelings bottled up express them!!
If he told you he liked you, then acts like he doesn't even know you exist when school starts, that should already tell you he's not the one for you and you should just move on. You will know when the right person comes along, it will feel just right and you will have no doubts about anything.
im 15 and no one likes me but im ok because until your 13 you should think boys are icky