Besides all the other great advice given here, the only think I could think of, is was he sexually molested as a child? That sometimes will cause theis type of behavior. Whatever the case is, it might not have a medical origin ie. physiological, but very well does sound like a psychological manifestation. I agree with taking him to a psychiatrist for an evaluation.

Until that point, keep a fresh perspective on it, you love him, you know this isn't right, stepping back and looking on it you can see why would anyone want to do this to himself??? Hope you can find the reason for it soon, and gain a solution as well.

hugs Lisa