Used to be in a situation similar to this.
Was w a girl the summer between junior and senior year. I was 17, she was 18 and going to college about 5hrs away from me at the end of the summer. At the time I didn't have my own car and had to borrow one of my parent's. The night before she moved out I told her I would only be able to visit her monthly at best, and basically friend zoned her in the nicest way possible. We kept in touch for about 2 weeks after she left, then I realized I was the one starting all the conversations, and I stopped trying to contact her. I have not heard from her since and that's ok.
OP make up an excuse to leave house for a day or two.
Tell her how it is. If she tries to make you feel guilty about not visiting her enough; leave.
If you want to take this seriously you will have to tell your parents at some point.