I get depressed at school?

Hi everyone.

At school I've noticed I get depressed easily. Normally I get depressed due to several reasons:

-Seeing my crush. Knowing that we'll never be in a relationship. And not knowing if he's interested into me or not.

-When I don't learn something or understand something.

-If I do something wrong, or don't meet someones expectations (such as my teachers)

-Kind of being lonely

But I also feel like it's sort of wrong, because at home I'm dis-respectful, mean, and rude towards my guardians. And at school I'm nice, and friendly - but this is according to my peers and teachers.

Does anyone know why I act that way at school, and different at home? Is it wrong that I act different at home? (I don't do it on purpose. And all my life, before my depression even - I've always been a nice student, at least according to my teachers and peers) And does anyone have any advice to help me not feel depressed at school?

Thank you.