Navy Girlfriend That Dont Know What to Do.

My boyfriend and i are 16 and 18 and although he doesn't leave until march. Being so young and all i never would have thought i would find someone who i truly care about as much as i do about him. Were planning on staying together thought everything. The navy recruiter is wanting him to become a swcc/seal and they're all telling him he has a very good chance. We've been together for awhile so i know i want to stay with him. It's just really hard and its all i hear about like when were together all he wants to do is watch the military channel and I'm very proud of him going into the navy because he has talked about it for a long time. He signed back in April before he graduated but why is it so hard on me even with him leaving in march?