Why Must Moving Bring Unwanted Emotions?

So because of school requirements, I now need to move back to California earlier than expected. Instead of moving back in the summer, I will be moving back in 3 weeks. At first I was stoked on the idea. But as the day draws near, all I can think about are the people I will miss here. It's crazy because while living here I kept thinking about all the people I left behind in Orange County. I guess it falls under the you don't appreciate what you have until it's gone category. I've made more friends than I had planned on making. I also got a lot more comfortable with the city and living in Vancouver than I thought I would. But working three jobs is one thing I will not miss. I love most of the people I work with at these jobs, but the hours are wearing me down. When moving the best thing to do is look at the glass half full. If it's half empty sooner or later it'll just be empty.