Most Helpful Guy
You can't forget everything about him, and you shouldn't. There are probably nice parts that you want to remember; after all, there are reasons why you initially got together. The bad parts. . . you want to learn your lessons from this experience, and you will think about what happened and reflect on it for a while and gradually decide what you did right and what you did wrong, and then you will be ready to move on.
When you get to college, you can transfer into another section of the same class if you get scheduled into the same section. Usually, you can't do that after the first week of class, so act quickly if that is a problem.
Most Helpful Girl
You can't. And the more you think about trying to forget about it, the more you are going to think about it. It sucks.
What you do do, is learn what you can from it, and trust me there are a lot of lessons to be learned from the whole ordeal, and figure out how you are going to use the knowledge you obtained to push yourself further in life. Life is all about progress, and to successfully progress you must figure out how everything in your life moves you forward. Never dwell on staying the same as the past. Every day brings you something that changes you, you just need to figure out what that change is.
As you progress, the feelings you want to run from right now, fade away and the memories become just components of your history.