Hi Jenna, Is your bf back still bothering him? Sometimes we don't realize the physical strain sex puts on the body and I wonder if it is possible that the act causes him physical pain? Some pain meds also not only affects a guy's ability to "perform" but also can cause issues with his desire.
One other thing, many of us "guy" types make our entire self image out of our work. It is not just way we do but for many it is what we are. A poor self image can also do terrible things to a guy's desire.
Again my best guess is that it has nothing to do with you, but may well be something physical on his end. Who knows a little teasing by you, and then a first move may be just the right thing. However, don't get your feelings hurt if he may not be able to "respond".