What medication is he on for his diabetes?
Thankfully, you are. Get a meter, see what his blood sugars are up to. Because when they're high, that can and likely will cause debilitating fatigue. If you can get the blood sugars down (which'll have to mainly be through diet), you can rule T2 out as a cause. It'll either make him feel better, or he'll have to get his heart meds adjusted. T2 affects the heart as well, so if T2 gets sortof done and dusted, it might help there as well. Try getting him on a low carb diet, see how that goes. Check the link in my signature for a little how-to, though you might want to adjust for his other conditions. Maybe more protein and a little fewer fats than one normally would. Lots of meat, fish, poultry, dairy, above ground green veg and the like...
