You may not realize how often this happens, but there ARE women out there who are unopposed to cheating and/or sending "Dear John" letters to their deployed men. A lot of guys have, unfortunately, been hurt by this.
Not only him worrying about you being faithful, but him worrying about you. Is he a career guy? Either way, it sounds like most of all, he's nervous. It's his first deployment, after all. He doesn't want to waiting on him in case he, somehow, some way, can't fulfill the obligations that puts on him (i.e. coming home at all). Rather than worry about you worrying about him, he seems to want to just get this deployment under his belt.
From the little you've said on the situation, I think you COULD end up getting back together. But you have to ask yourself you are really up for it. He's given you a clear, guilt-free way out if you aren't. If you do want to be in it, though, I'd say just support him. Write him letters. Send him care packages. Skype with him. And work out the details when he comes home. The most important thing is not to force the relationship on him, just be supportive.
But also be prepared for the fact that he may legitimately not want a relationship, either now or when he comes home. Like any other relationship, you're going to be risking your heart in this.