Hi, I understand your situation completely. My father was an officer in the Air Force for 22 years. We hit a move at a particularly bad time for my younger brother at 17 as well. We had been living in Lawrence, Kansas for 3 years when my father was ordered to Nellis Air Force Base in Nevada. The move did not effect me, I was in my second year of college, but my brother had his senior year of High School left and was not happy about having to leave his friends.
My parents weighted all the options and decided that a high school diploma from Lawrence, Kansas would look better on a college application than one from a Las Vegas high school. Besides they had already decided to retire in Lawrence, so they would not have to sell the house. It was a very tough year for them. My mother stayed in Lawrence with my brother, dad moved into a studio apartment in Vegas, and I was in college in Ohio. We kept in touch with family conference calls every Sunday at 10 am for a year.
Since this is your son's senior year in high school I would discuse his plans for his future and how the move will effect the entire family. I'm not sure just staying for a girlfriend is a good enough reason to stay behind, but he needs to come up with a plan on how to make this work with you and your husband. Make him understand that if he stays behind you have certian expectations about how he conducts himself, where he lives, and make sure he stays in school to get that diploma.
You might also point out that this is his last year to be able to experience an adventure with his family. Alaska is a place not many people get to explore. As an Air Force brat myself I have come to appreciate the unique learning experiences that my father's career aforded me growing up. I was able to go places, learn about different cultures, and see the world in a very different way than most teenagers. He might not appreciate this right now, but I think in the future he will discover that he misses the excitement of going somewhere new and starting fresh.