Bootcamp

Soo I need some advice I met this guy and started talking to him not long into our first conversation he told me he was leaving for Bootcamp for the marines in a month. Everything was good and we made time to see each other as much as we could up until the last few times we saw each other. I think he was talking it hard that he was leaving. And like after he left I kinda realized that I just don’t think he’s my person our goals just don’t level out and I feel so bad because he wrote me a letter and I’ve been pushing off writing him back because I just don’t know how I feel and I don’t want to give him false hope. But I also know he’s going through a lot right now and I don’t wanna send him a shitty letter about how I don’t think we’re endgame. I really just don’t know what to do. Do I send him a letter being just general and updating him on my life or do I just lay it out that I’m not sure how I feel? I’m not dating or anything while he’s away mostly for personal preference but also because it feels wrong especially because he told me he couldn’t wait to come home to me in his letter. It’s all just a little heartbreaking and I’m at a loss on what to do. He’s a genuinely nice guy I just don’t think he’s my guy