Feels weird trying to give you advice as I'm pretty sure I'm the one who should be taking advice from you.
You're leaving for college in the morning. I know tonight feels like the end of life as you know it but I promise you (I PROMISE!) it only gets better from here. It sounds crazy now but pretty soon you will forget almost everyone from high school and the thing about it is... you won't even feel sad about it. Why? Because you are going to meet some amazing people and experience some amazing things.
It is sad to think about all the friends and acquaintances you will never see again and this will be a reoccurring theme as life goes on and you move from chapter to chapter. And even though life won't always turn out the way you'd hoped it would, you will always be blessed with great friends wherever you go and they will make every experience richer by their presence. Some will cross your path for only a short time and others will stay with you for life but rest assured, one constant in your life is fabulous friendships.
You are such a good person. It amazes me. As disappointing as it may sound, I wish I were half as good as you are. So, trust that you are good. Trust that you are great. One of the greatest days of your life is when you realize that you are great just the way you are. Forcing yourself to like Dave Matthews Band (at least more than you would on your own) just for the approval of a boy will one day seem just as absurd as confessing to the boy you like that you are a mega fan of Backstreet Boys (and seeing them in concert will, indeed, be one of the best nights of your life). Which leads me to the next thing I must tell you.
You aren't always going to make great decisions. There will be a lot of things you will be able to look back on and regret but you know what? Don't. Don't regret anything. Like the fact that your mantra in college will be "C's for degrees!" and you will heartily adhered to it? You won't have to regret that because college will be damn fun and the social and emotional education you get there will be worth more than a 4.0gpa any day. Be La Belle Dame Sans Regrets!
Now, having said that, pay attention to the most important piece of advice I will give you: Never underestimate yourself. Don't put limits on yourself. It'll take a lot of fear and a lot of difficult situations (ie training for a marathon) before you realize it but you are capable of WAY more than you give yourself credit for. You can do anything! It's amazing what dedication and consistent hard work will accomplish.
So there you have it. Go forward. Be brave. Be amazing. You already are. It's just time for you to believe it for yourself. Cheers!
the 31yr old version of you