My boyfriend is having the same problem with a Valencia orange I got him, except he doesn't keep his dry. It lost about half of its leaves in maybe two months, and just started to bloom last week. Not sure what's going on, but I have read that citrus' don't like adjusting to new conditions and will protest by dropping leaves. Try putting your tree in the sunniest window you've got and mist it once or twice a week to keep the humidity up.
