Emission Systems And Parts

I work at a store, so it's not like my future career or anything, but when I was hired, I had said that I wasn't a student, and therefore could work anytime.
My life has changed, however in the last few months and now I go to school full-time as a nursing student.
I work 2 days during the week, which isn't bad, but now that my husband works nightshift, I have to take the bus home, which requires me to wait at a bus station for over an hour late at night (our bus system sucks).
Anyway, I am scared at night, especially since it's a bad part of town and also, I'm exhausted in the morning when I get to school.
I just feel bad about having to quit, like I'm letting my manager down.
I know I'm completely replaceable, but still....