Cut it any way you wish, but a break is a break up, so instead of waiting for three years on him, enjoy your freedom to explore, experiment to your hearts content. He has a commitment, and there is no telling where this will lead him, so live your life and be as open to your own options, opportunities, and possibilities as he is, and more.
You deserve this, and need it, so take advantage of it, and don't waste your time on any cockamamy scheme to get him to concede to any temporary agreements, or commitments to each other so far in the future. Thats crazy!
Live in reality, and enjoy it, not fantasy, and worry. He has left high school behind, so should you. As an adult, you have to realize that the realities of life changes even the best plans.