First, let the past go. This is important. It can't hurt you any more, don't let it humiliate you. It is nothing. Those memories are unimportant. It's okay to let it go. To forget.
If you haven't yet, you'll soon meet the boy that will ruin everything for you. Don't let the tears, jealousy, lies, and pinpricks of angry pain get inside of you. The things he'll convince you to do. Don't let it hurt too much.
One day that too-wide, too-thick, too-red smile will make your stomach heave with just a thought. But you'll get through everything.
He's not going to break your heart-- you'll stop loving him long before-- but he will break your spirit. And it will hurt.
But the haze you spend the next few years in will life. You'll say, Enough. After more tears and fear and guilt, he'll be gone.
You'll always feel guilty because of him. Dirty. But allow yourself the beauty of your strength. Your determination. Your heart. You'll pick up the pieces and move on. Not always in the right directions, but at least in better ones.
And one day things will just click. The past won't matter so much any more. It will still hurt, but it will be dull, distant, forgetting.
There will be a lot of tears and depression, and many boring days and nights, but life will be better. Not the way we'd like, but better all the same.