Unfortunately, we can't tell you what to do. I suggest to help you make your decision you look at the facts:

1) You started dating yesterday. Yes, you had a crush on each other for a long time, but the fact of the matter is you didn't actually enter a relationship until incredibly recently. That doesn't give you much time to bond as a couple before

2) He leaves in a couple of days. For three years. Three years is a long time, especially in high school, when you are both going to grow and change so much over the next few years. People are rarely the same person they were at the beginning of high school once they have completed it.

If you think you're up for this commitment, go ahead and make it with him. We don't know you and we don't know the resolve of and strength of your feelings. I will warn you, though, that long distance relationships are incredibly difficult. Sometimes it's easier when you've known each other in person rather than starting an online dating relationship, but it's never easy. You will each see each other's lives move in different directions and you'll wish you could be a physical part of it. Unfortunately the reality of it is you have to make do with what you can- phone calls, letters, text messages, social media, and video chats. Sometimes it DOES work that way- I know there are people on this site who were long distance with their partners for many years; you might want to hear from one of them for more experienced counsel. Just be aware it can be hard.

Whatever you decide, the decision has to be yours. Only you know your feelings and only you know your willingness to try a long distance relationship. My hope is that, whatever you two decide, you can still manage to be close to one another and hold a special place in one another's hearts. There's no reason why that can't happen.

Good luck and PM me if you need anything else. I'm here for you.