So I’ve been with my boyfriend for around 3 years now, and this year he’ll be graduating and entering college while I’ll still have another year of high school. Any advice on how to handle the situation?
SKYPE!!
Think about what you’d want to have happening if your situations were reversed; that is, if you’d want him to encourage you to follow your dreams if you were the one graduating, do that for him. Don’t plan around each other. If he wants to go to a school far away, support his decision and assure him that Skype, FaceTime, etc., will keep you in touch while he’s gone.
It’s rare for high school couples to stay together for the long haul, but it does happen. Your best shot at that is making sure that both of you are planning your lives for what you ultimately want aside from each other. If he stays at a local school because of you, he may end up resenting it (and you). Be his biggest cheerleader, tell him you’ll miss him terribly but would never dream of holding him back, and then see how things go after he leaves. If you’re meant to be together, you’ll figure it out.
And once it’s your turn, if you’re still together? DO NOT pick his school unless that’s where you’d be going even if he didn’t exist. Again: if you’re meant to be together, you’ll figure it out. Your job at this age, though, is to figure out your own future. 
You guys should have an honest conversation about whether you are staying together for college or not. Freshman year is full of new experiences, and sometimes having a LDR can significantly affect a person’s ability to fully immerse themselves in the life of the college.
You won’t like my answer. I suggest you both agree that this is a time to take a break. If you are meant to be together, you will make it work. Whatever you do, please do not make,any college plans around him. Apply to the colleges you are interested in, regardless of where they may be in relation to him. Good luck.
Totally agree with @Lindagaf. Although it is difficult to hear, you need to find your own path first. Hang in there and enjoy your senior year next year and going through the college process.