Hi HZ3006,
I'm sorry if I missed it, but what makes you think that your boyfriend only wants to be together until high school is over? Have you discussed it and he said those words, or are you assuming?
Sometimes we assume things. We are quite often wrong when we make assumptions. That is a fact of life. Perhaps this is the position you are in right now. If so, sit down and talk with your boyfriend to relieve your worries.
If you and your boyfriend have openly discussed plans after high school, and your belief is fact, it's a matter of acceptance. You do have decisions to make. It is your decision whether or not you want to be with him now, but not later. You also have a decision to make on what kind of relationship you are comfortable with. Maybe you should break up, but remain friends. Maybe you should completely break free. Maybe you should stay together, and love each other until the end. Those are decisions for you both to make.
I really don't find your Q's and emotions weird or unsual ~ you have every right to feel the way that you do. Your emotions are valid. That said, your emotions don't need to rule every decision that you make in your life. Use the emotions to your advantage, to help guide you to understand what is actually important to you. From there, use your wisdom to get through the problem with as little complication (bad feelings) as possible.
Best wishes and

to you!