I'm still here because of a classmate of mine
What did the classmate do to get you to stay?
They told me they would miss me if I left.
It's nice that you considered your classmates feelings before deciding to leave but you shouldn't have stayed if they were the only reason. You may have missed out on a great opportunity and it was wrong of them to guilt you into staying if you wanted to leave.
Next time I will just leave without letting them know.
Tell your friend if you leave, that is the polite thing to do.