Sex with clothes on

Everytime my boyfriend and I have sex he keeps his shirt on, my bra and shirt on, he won't even take off his boxers during sex. I know he's ashamed of his body so I think that's why he won't take off his shirt let but I've seen him shirtless and he looks perfectly fine to me ;). What I don't understand is him not even taking his boxers off. Sure it's cold where we live and all but I don't understand his reasoning, since he keeps the room a nice 80 degrees for me (always cold)