For me, the last day of school really opened up my eyes how nice people were. I regretted not making the most of my high school years and shying away out of perceived rejection. That day, I just really wish school wouldn't end and I would have one more moment of this. I mean, I had been with these people for the last 10 or so years. After this, there would not be another year of normal school.
I think I also had that longing for school to continue because I dreaded college. I had no idea what it would be like and it would be my first time living on my own. But by the the 2nd or 3rd week of college, I had pretty much forgotten that bittersweet feeling.