I had to reply to this problem you had because it reminds me so much of my current situation with my ex/boyfriend (delete as appropriate). Like you, I got with my boyfriend when I was quite young - 18 - and now I am turning 21 and he was also my first love and the first man I made love to.
We literally mutually broke up yesterday, there were a lot of tears and it was very painful but it is here where I agree with your guy. You need to understand the fact that he says YOU ARE THE ONE HE WANTS TO BE WITH, now this might change but it is this that you need to go on for now. I can tell you that if you don't give him space to go out and be his own man and, I hate to say it and I know it is painful because I know it will be for me, sleep with other women. He will grow as an individual: he will know what it is like to hurt and laugh and improve as a man and a lover and as much as that might hurt for you you might find it to be worth your while in the long run if you support him with this decision and start making you way in the world on your own too. You might find that, even though it seems SO unlike now, that he is actually not the one for you.
You are young.... seriously: going to college will bring about so many encounters and experiences that will make you grow as a person and clinging to something so familiar will hold both you and him back, trust me, this is what I am experiencing now BEING in uni even though I know that when I am older and want to settle down our situation will be perfect.
Mate, you can't set a time limit on these things, it is a natural progression and he will know when it feels right. The way I see it, you need to just let him go, not for good, just for now, and dive in to new people when you go to college: trust me it is SUCH a laugh, once in a lifetime. He might be perfect for you and you for him but trust me, if I was in his head, as his mentality seems a little like mine at the mo', he really needs to experience the hurt from other girls and situations to fully appreciate spending his life with you, it is only then that he will be a proper man for you. TRUST ME, this grey area is not fun, as i'm sure you have realised, its not heathly and feels more like an addiction, a routine, than a relationship.
Me and my boyfriend are broken up, its official, but we'll still be cool with each other, content with that fact. And, even though it hurts, objectively, the decision is best for both parties. Yes I will go out, flirt, have sex with other guys probably get hurt in the process but become a better lover and find out more about myself: my view and opinions and attitudes to people and the situations that life can throw at you. He will go and build his qualifications, his career and his strength as an individual and eventually, when he gets over me, his sex life.
Then, we will meet back maybe in a few months, maybe in a few years, and have a serious discussion about whether the way we have changed and learned for the good (or even the bad) makes our lives meets together. It's as simple, however painful, as that. I think you should seriously consider yourself in this situation as your own person NOT as a person in relation to how he thinks and how he feels. You might be surprised with what you come up with. I'd be interested to know what you think about this.