I think you have to know your kid and whether or not they are the kind of kid who will thrive at boarding school, grow with the independence, and get a good experience out of the rigorous academics, or whether they are the sort that needs more guidance. It can be a great fit for some kids, and not such a great fit for others. I realize it's hard to let your baby go, but I find some of the judgmental remarks on this board every time boarding school comes up to be kind of off-putting. I know plenty of great parents whose kids attend boarding school--including a kid I babysat for who wanted to play hockey at a higher level, was extremely independent, and didn't fit in the social environment of her local high school and attended Choate. She kept in touch with phone/Skype and remember breaks are longer at boarding school. It was a very good fit for her. Other people, not so much. But don't let other parents guilt you over being a bad parent because your kid goes to boarding school. For the right kid, it could be a great experience.
At that age, I think the kid should have a say about whether or not they are ready to leave the house. If your kid is ready and your DH is on board and you are willing to pay that much, then go for it. If your kid seems ambivalent and you get the impression your DH is pushing him into a situation he might not be comfortable with, luckily there are some great prep schools in DC where your kid can get a fantastic education. There are all kinds of ways to be a close family.
Don't worry. Given the state of parenthood around here this is the last of the poster's worries.