How do I keep going?

I hate school so much. I have no friends because of severe social anxiety. Everyone says to take it slow and do exposure therapy, buy I feel like crying if I even think about talking to someone. I feel like I'm bit even physically capable of approaching anyone. I desperately want friends, but I can't bring myself to make any.

I went on this field trip thing because my school thinks I'll be a good engineer or whatever. When I was on the roof of the building, I couldn't help but be enamored by the height. I thought about how I might die if I jumped.

I just need to get out of school. It's ruining my life. My stupid ADHD doesn't help. I've gone from straight A's and highest test scores in the grade to average grades. Maybe even some below average. I got a D. That's horrible. If I keep going like that, then I'll fail the class and I'll have to repeat it and I'll never be anything in life so I should just kill myself. I'm so disappointed in myself. I never thought I could do anything below the best, but now I'm doing horrible. All because I can't turn in work.

I want to be done with school. I want to be done with everything. I want one real life friend. I haven't had any for the majority of my life. I know it's stupid since I'm only 15, but I feel like my life is nearing its end.

I've already waited so long, but I guess I can hold out for 3 years until I'm finally done with school and can move out.