My "best friend" is ignoring me.... help? sorry its lengthy -_-?

okay, well to start this off i have to say that i met this boy, ill call him tyler, in 7th grade and ever since then we have been great friends. "best friends" some could say. (im in 10th grade now btw) so we would always text and talk everyday. never calling over the phone but just texting and when we saw each other at school. it was the kind of thing where we would just make fun of eachother constantly... in a good way haha. also, soooo many people thought we were dating, which we werent. but i did start to like him and after awhile i told him that i did. that was the begining of 10th grade year. and ever since that, its been going down hill. first, during our P.E. class he started hangin out with other friends and being a total jerk to me. like sincerely making fun of me and bringing up stuff that i thought he wouldnt ever bring up. and that was when he was hangin out with his freshmen friends. ( hes in 10th grade also) then after that for a few months he was all friendly and flirty again. but now this semester, just all of the sudden, hes totally shutting me out. we have a bio class together and he used to turn around alot and we would talk almost across the room, but now he literally wont even look at me. sometimes i catch him glancing but i havent talked to him for about 5 weeks straight. and that includes going to his house everyday... ( we carpool for swim practice) and again, he is hanging out with his freshmen friends. its like he cant be with two groups of friends. he can only be with one at a time. and some of my friends asked why he was ignoring me, he said he wasnt, then another time he said i was ignoring him!!!! it makes me so mad!!!! sorry this is so long, but finally to my point. Why would he do this if i was his "best friend"? he would even tell me i was his bestfriend/his other half. now its just totally stopped. it pisses me off. so any idea?? guys point of views maybe? ThankS!! sorry its so long!