For sure, it may hurt now, but in the long run you are better off without her. Trust me, especially since you are still in high school (assuming since you have a car), that there are much better things to come. I know it's gonna suck, but try not to think about her or what she's doing.
Involve yourself with something else, maybe even someone else. Take what you have learned from this relationship and apply it to other ones so these kinds of confusing situations aren't as confusing. You'll be fine, I know it, and if you're going to college soon, you'll be more than fine.