Is it normal to always be thinking about your best friend?

I am a 19 year old guy and a freshmen in college. This girl I think about almost everyday is at the moment my "best friend". We went out in high school for a year and had been friends before. Our relationship has always been complicated. Sophomore year of high school we started talking to each other and became very good friends. She would come over my house everyday and we talked nonstop. Junior year we started going out and broke up by the end of it. After that, we would talk on and off because of various problems and feelings. Recently, she came back from college and of course we spent every day together. We had long talks about our relationship and decided we were best friends. I told her I love her and she said the same. This girl is probably the most important person to me. I've been thinking about her for the past couple days since she went back to college. The title is best friend, but I love her. To clarify: I love her as a person that I never want to lose and hope that we will always see each other as special. So...Is it normal for me to be thinking about her a lot? Or do best friends just call each other sometimes and have a laugh every once in a while?