I'm not sure what you mean. Do you mean that he doesn't take his shirt or boxers off infront of you, or that he doesn't take his shirt or boxers to have sex (
He might feel a bit awkward, I know I might. (I have to get used to it infront of other people almost every school-day next semester, b/c of junior high)
Just continue your relationship as normal. He will get used to it. One time just ask him to take off his shirt/boxers. If he says no, then ask one more time. If not, then let it go. He will eventually do it.