HOW DO I STOP THINKING ABOUT THIS?

I'm at the school library right now trying to study for midterm this wednesday. I feel like I'm about to break down and cry. I keep thinking about this guy I used to see. I don't even know why. I hate everything about him. He doesn't go to school, doesn't work, and doesn't have any plans for the future besides sitting on his a** and watching Family Guy. HOW DO I STOP??? I'm a strong girl. Tears are a sign of weakness? Tips? THANKS!!!