I need help n advice

Hello! Today was my first day at the last year of highschool and I was hoping I could do a fresh start because I want to achieve top scores this year. This might seem stupid or unmature, but my bff or former bff didn't sit with me, and that made me go to a whole another world of sadness. This friend is like my (everything), he was the closest person to me ever and I felt the happiest human on earth with him, but because of some reason, we lost contact a little, and when I gone to face him about it, he said i am the one to blame, he pulled himself away because i didnt give him attention or anything, I was depressed last year because of some mental health problems and because of me being diagnosed with ADHD and being helpless + the mental weight of the final year. I tried to explain that to him but he says that dont justify it and hes sorry for that, ever since that happened, i became so sad, I didnt leave Home, I couldnt face my friends, I dont go to hangouts anymore, him saying that made me feel shit about myself and how horrible of a person i am, I was hoping like we could start over but he says the plane has already took off, he like greeted me in school and talked about math n all that but it just doesnt seem the same to me, its like he hates me and only talk to me because of our other friends, im scared if I open it up to him ill be labeled as a toxic person or a dramatic person, but its just this whole thing make me feel shit about myself, I couldnt focus on any of my classes today because i was thinking what should i do, my head hurting all the time and almost feeling like its gonna pop, I dont know what to do, I just want to feel happy again, but i realised i cant ever relive the same happiness I had because of what happened, please, tell me what to do, im so completely lost and speechless, please...