Sorry OP, i hope that book helps. Are you sure he isn't hiding a problem in shame ? By that I mean maybe there is a medical issue he is hiding he knows about like having a tough time keeping an erection and so he avoids it at all costs? There are many possible physical causes from heart disease, to antidepressants, to alcohol or drug use, to low levels of testosterone. If he’s ruled out other factors it’s a good idea for him to pay a visit to his doctor.