Why does he want to leave me after so long??

Did he say why he was breaking up with you? This sounds like either you broke his heart or someone is in his ear about you. Someone so in love does not walk away like that for nothing.

He could be trying to protect you or himself from getting hurt since he is getting ready to go to college. He may just need some space or you could be to mothering for him. there could be alot of reasons why something can happen so sudden. It may be sudden to you but that doesnt mean that it is sudden for him he may have been thinking about this desicion for awhile the best way to find out is to talk to him even if he doesnt want to.

he's got issues.  you've only known him a year and theres already drama.  A year is not long to know someone.  Love is so much more simple, I think than what we make of it.  I know, and you know of people who really love you and its just easy. you breathe in, they breathe out.  you can count on it.  Thats real love.  Love isnt flakey or confused. I would move on.  You'll drive yourself crazy trying to figure him out.

Since you indicate that he will be going off to college, I can correctly assume that you are both young. For you both, life is extremely dynamic with many changes to you personally and to your worlds. I am sorry to say that I don't think there is much you can do. At college he will be exposed to new people and experiences. He needs time and space to find himself. This is an extremely difficult period for you but I hope in time you too will meet new people and change your outlook abd expectations. Life is full of experiences that often require the ability to overcome the difficult. I wish you the very best.

CC ,  He may love you , but isn't in love with you , these are two separate things . A couple things in your question jump out at me , him telling you he doesn't want to be miserible for the rest of his life and him changing things for you .  What things ?  Did he change for you and become someone he really isn't , someone he's not comfortable trying to be ?  He's told you he doesn't want you in his life , you can't make him love you .  He's cut you from his life , so I think it is time you do the same with him . I know this will not be easy but you need to move on .  The two of you do not want the same things out of life , which will cause resentment if you were to stay together . Some of this could be related to the stress and unknown of his starting college . When you love someone and want to spend your life with that person you cling to one another and face problems together , love is not confusing , it is simple , with the right person .