Happens... ever see "Full Metal Jacket"?
Going through Marine Corps Boot camp changes people for life. Even if the change isn't immediate. Soldiers also have some very strenuous training, and trust me, it gets VERY mentally invasive... .it changes everything about you.
Ask him to make a list of short term and long term goals. When you're not in them (excpet "get married" and "have children") then you need to re-explain the facts of life to him: You're a lady and you need date nights, weekly surprises that don't cost a thing (letters, breakfast in bed, etc) tell him he'll get back from your relationship what he puts into it.
But whatever you do.. don't mention my name to him.... lol I don't want him to come looking for me.... lol
I'd still do it... especially if he's leaving... things like daily letters, he can still surprise you, but it would be far more difficult.... but it can be done....
He'll never adjust back to whom he was... but he can adjust to whom the two of you shall become, if you both work at it. Getting him to open up will be very hard. Perhaps the easiest way is to listen to him when he's around other military personnel, then ask easy questions later--don't probe, just be interested. Get him to tell you things the easy way... don't drag. It won't be easy... and good luck I wishe you the best.. :D