You seem like a thoughtful young lady. I think it is reasonable for someone your age to need some space and I think you just be honest. Tell him that you do love him but need some "you" time to focus on X, Y, and Z. Tell him that you hope that you can come back together after this time but that you just need a bit of space.
good luck. (by the way, it is always hard to hurt someone that we care for. It will be difficult. But if you do it with no malice in your heart and are genuine, it goes much better. You sound like you neither have any mal intent and are sincere. This will help you through it.)
Just be honest and sincere, chances are he may be having the same exact feelings as you and it will turn out to be a mutual decision for both of you. At your age, stay away from relationships and have fun.
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