leaving boarding school halfway through junior year? need advice.

You need to be getting some adult help ASAP, does your advisor know that you are crying every day and can’t sleep? Do your parents? Can I suggest going to the nurse or whoever you got to there and talking about exactly what’s going on and honestly how you are feeling. There must be a counselor or therapist at school you can speak to, 3 weeks is too long to be going on in the crisis mode you are describing, please go talk to someone.