#8 says it very well. Relationships are generally much more fun at the very beginning. If the relationship does not make you happy now, then chances are it never will.
You have a lifetime ahead of you; this is probably not a decision you need to make right now. You should tell the boy that you are not feeling ready to make this decision yet. If he loves you he will wait for you to figure things out.
You should be living in the present, concentrating on finishing high school, and enjoying being there. Tomorrow will come, whether you worry about it or not. Enjoy today and take things slowly.