I am a former Marine and have deployed to both Iraq and Afghanistan. First issue: don't try and stop him from enlisting. He's probably doing it because he thinks its the right thing to do or out of a passion for public service, and that would only cause him to resent you. He was not lying when he said he wanted to stay with you, but he's still going to look at all of his options.

Second issue: I assume you are opposed to him enlisting because you don't want to be away from him. The truth is that you probably won't be able to see each other very often. You'll be near him more often if you marry, but that is probably not a great idea. From my briefings in his position, 80% of first-enlistment marriages end in divorce. The stress of being on active duty is just too intense. The hours are long and the conditions are hard. He will be under extreme pressure to perform.

Life in the Marine Corps is hard. Boot Camp is 3 months long, followed by additional training, followed by a permanent duty station and possibly deployments. Training is difficult. In the fleet he will be treated poorly. He will never catch up to the lifetime earnings of someone that started working right out of high school. I suffered multiple injuries that still bother me, and that is the norm rather than the exception.

All of that being said, I don't regret it for a moment. It was the right thing to do. It was an experience I would never be able to have anywhere else. But it was undoubtedly a large sacrifice. The recruiter will talk about the good and he's not dishonest to do so. For the most part, recruiters are not the dishonest people they are made out to be. You remember the good and the bad, but its the good that you look back on most of the time.

Your relationship will probably not survive his entire contract. I wouldn't blame you if you decided to end it now. I also wouldn't blame you if you decided to try and make it work. This part is entirely up to you. You are 17 and have your entire life ahead of you. Either choice will be difficult, but you are young enough that you will be able to recover.

One last thing

It may be relevant that at the time he wasn't sure he would qualify due to a bolt in his knee and multiple concussions. He sounds like the type that can handle the lifestyle just fine. Good luck.