this is my last year of high school and I really want to stay in touch with my English teacher- we’ve gotten quite close however I’m just not sure how to ask in a way appropriate at school ??

This is fine to stay in touch.  Just ask if it’s okay to email them updates after you leave school.  If they are uncomfortable with it, they will tell you.  I’m sure they will appreciate hearing from you after you leave.

this is my last year of high school and I really want to stay in touch with my English teacher- we’ve gotten quite close however I’m just not sure how to ask in a way appropriate at school ??

This is fine to stay in touch.  Just ask if it’s okay to email them updates after you leave school.  If they are uncomfortable with it, they will tell you.  I’m sure they will appreciate hearing from you after you leave.