I strongly hate my high school p.e class, for many reasons. it worsens my depression. could my therapist be able to write excuse to exempt me from p.e?

Actually, PE: activities improve your physical and mental conditions. Talk to your PE teacher to adjust your level of activity which you will enjoy.

Possibly however...: In general exercise and physical activity can really help depression so I encourage you to be more physically active. I don't know the reasons you hate your PE class but advise you to discuss the reasons with your therapist. If your therapist agrees it would be wise for you to avoid that class he or she can write an excuse, but I have no way of knowing if your school would accept it. Good luck!