I'm in a new and great relationship, with a great girlfriend, why do I have thoughts of wanting to break up?

I knew her for about 8 months before we officially started dating. We are both college aged. I just graduated in December and she is due to graduate this coming December. I'm not afraid of marriage or opening up. She has all the things I look for in a girl: positive, smart, good communication, well traveled, great smile, physical attractiveness is on point too! We have been together for about 4 months and I could see this being an even greater relationship than past ones bc we share just enough in common that we aren't totally the same but can still introduce the other to new stuff. We have weekly bible studies, just the two of us, that have really brought us together too. So, why do I keep having these flight feelings?