Has he been checked for low testosterone? It can affect libido as well as other mental things and even make men more vulnerable to depression. I was a little skeptical of that, but I went from being a very driven, aggressive guy to being what seemed like a different person, very withdrawn, as my T levels waned (when I was around 46/47. I also went from having a very high sex drive to very little. Getting T supplements really improved the situation.
