3 year relationship now seperated by college

My girlfriend and I have been together for more than 3 years, almost 4 now. We began dating my freshman year of High School and I am now a freshman at a University. After being together for almost 4 years, we've become best friends and have done everything together, I even gave her a promise ring at the end of the summer. I care a lot about her and I don't want to hurt her but I have noticed that after being here for only a month that some of those feelings have subsided. Naturally the distance is going to complicate things but this is very strange for me because my feelings never changed all throughout highschool, not even once. There's also a girl here that I've been hanging out with on the weekends, not alone, but just in a group of people and I'm starting to develop a little crush on this girl, nothing serious. But my question is what should I do? If I find myself losing feelings for her and gaining feelings for someone else after only 1 month then that must mean we aren't meant to be? But she is still madly in love with me and I really don't want to hurt her, I suggested once that we take a step back and think about the reality of our future together she immediately began to cry. She is still my best friend and I know that if I were to still be home with her none of this would be happening, but unfortunately it is... I really don't know what to do.