[Superman]

Many good comments here, possible causes. My suggestion is a bit outlandish, unprecedented and ill-advised: Why don't you talk to him. Sure, I know the subject has been raised but if I were you, I'd want to understand the details, the sources, the causes. Talking is one of the two most intimate things two people can do. Talking about the 'stuff' that bothers us or embarrasses us or reveals us, and then finding a sympathetic ear and forgiveness, takes intimacy to a whole new level. Many guys do not know this, and have trouble with soul-searching and discussing intimate stuff. It'll work if he will come out of whatever shell he might be in. I mean.....it'll work in the sense of finding your answers.