I know at your age (and I don't mean that as a put down, but having once been a teen and remembering what its like, I can say that. ), its hard to see our friends take different paths.
My very best friend in the entire world got married 2 weeks after we graduated from HS and I left the day after her wedding to go to college.
I started crying as I was walking down the aisle and heard later that the congregation in the church could barely hear the minister over my sobs. I cried through the reception and the after party as well.
My whole life was changing, she was starting a new life with her husband, I was going off 200 miles away to college and I thought I'd NEVER have the close relationship with her I had had in HS. Well, I didn't. But the relationship evolved over the years and I can say that even though we don't see each other as often, when we get together, its like we've never been apart. We have now been friends for 31 years! And I envision us staying friends at least that much more.
I currently have another friend that is starting a new chapter in her life. I'm not sure that I agree with her decision, but she is so estatically happy, that I find it very hard not to catch that enthusiasm when I talk to her. She's happy, so therefore, I am happy for her and I keep my reservations to myself, because I now know that to voice them, would alienate her. I just want her to be happy. And that's a hard thing to learn.
My own daughter has made decisions that disappointed me. Not that they were bad decisions, but I had MY own plans for her life and she quite rightly had her own mind about what she wanted to do. Accepting that her decisions were right for her (and they were) and being happy for her about them was THE hardest thing I've ever done (well there have been 1 or 2 other really hard things, but this ranks up there). But I had to be happy for her, even if I had to convince myself over and over in my mind (I will be happy, I will be happy, I WILL be happy) because I want her to know that I support her in most things. (not some of the boneheaded things, but she's proven time and again that what is right for her, isn't necessarily what would have been right for me at that same age).
I KNOW (believe me I know, I still have my memory of when this was said to me and I've said it to my own kid), that growing up is hard. And adults typically don't fully understand or have forgotten what its like. But here is the over used, trite part of my speech: You have to learn to accept your friends and their decisions even if its not something you'd do or you think they should do. It's their life and if you want them to remain your friends, you have got to learn to let a lot of this stuff just go. Quit hanging on to some of this baggage. Believe, me, I pulled massive baggage around with me for years, before finally deciding to get rid of it. So just try to be happy for him and if you can't, then pretend. Because sometimes, we all have to plaster that darn smile on our face whether we like it or not, or we end up ruining the best day of someone's life (like I did at my friends wedding by crying like a baby for 4 hours).
You are a very smart, mature girl and I realize that part of what you are going through is the learning process we all did as we become teens, young adults and adults.
And I'm not discounting the fears you have for your friend. We are at war, but he's got at least 4 years before he graduates from Annapolis, but he's entering a career that does carry risks. But so do a few million others. Firefighters, police,etc. And he's standing up for his country and believe me, that is a very brave and selfless thing to do and I applaud this young man, because I know that he's doing something I would have never dared to do at that age (or any age). I admire and respect anyone that not only becomes a part of this country's military, but has the skills, leadership ability and brains to get an appointment to one of our service acadamies and apparantly what it takes to become part of the elite SEALS. And the guts. AND he's doing what it is he wants to do and believe me, I bet from a show of hands here that not a lot of us ever get the opportunities to REALLY do what it is we WANT to do, but rather settle for what we need to do or have to do.