Clingy boy is not letting go?

So this guy at work is leavin for bootcamp soon and he started texting me. I liked him a lot at first, but he started getting clingy and im not feeling him anymore. We went on 1 date and i think he might think we are bf/ gf but we arent! He keeps telling me he will write from bootcamp when he is gone and then he will visit me in college. I dont know how to let him down nicely through text but i also dont want to be bound to him all summer. Can i get some advice please?