Chriskey, it's a depressing feeling isn't it. But it happens to all of us at sometime or other - frequently more than once - and it is recoverable.
I've always found that time and distance is the best cure. If you can't have physical distance (like if you go to the same school), then go for emotional distance. Also, remind yourself of this person's bad points.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.