You haven’t done anything wrong. He’s getting ready for deployment, and everyone does this in their own way. Sometimes people will move to strengthen commitments when there’s going to be a separation. Other times people will cut them off when there is going to be a separation. Your boyfriend is cutting off because he doesn’t want to hurt himself or you knowing he will be unavailable to you for a year while he’s in Afghanistan.
Respect his decision. Be sad and miss him, and send him letters and little gifts that don’t pressure him, but that let him know you’re thinking about him while he’s serving the country and away from you.
I hope that helps.