ABSENCE OF INTEREST. Suggestions.

Iam asking this question on behalf of my husband... He has a well built and healthy body. But it's been 2 yrs that we got married, he has never shown any attraction or arousement, neither any interest in physical relations. I have not seen or known him secreting the semen or masturbating. What could be the issue with him. I have tried to ask him many times. But he is so reluctant to open up. Would he be having any physical issues. He eats all kinds of foods. He doesn't work out much. Also I have done psychological sessions with him. Doctor has told that he is turned himself numb and is very reluctant to treatment. He has shut all his emotions down. Has such issues been found before in any other cases and what would be the possible reasons and what treatments would he need. Eagerly awaiting suggestions. Thank you...