Black stool can often be from bleeding in the GI tract. A GI bleed can cause anemia, and that could be causing the fatigue and hair loss. I would suspect that your husband does not want to go to the doctor because he either has a stigma about getting a colonoscopy, or maybe he is afraid of the possibility of cancer. You did not mention your husband's age, but GI bleeds are not uncommon and can often be controlled with medication. Maybe your husband will be more willing to go the MD if he knows that there are other possibilities to his symptoms besides cancer. Good luck
How old is he? How long has this been happening? There are different things that can cause black diahrea, but I would recommend he go to a doctor. Why does he not want to go?