Why do I keep crying???

So i just turned 18 and i have been in a relationship with my best friend for 2 years. We have started argueing over stupid stuff lately and i feel we are drifting apart but we still feel so strongly for each other when we are together. I also just started college. I have began to become overwelmed and today especially i have cried about almost everything. Why have i been crying so much lately? Anyone have suggestions?