For about a month now, my husband has been complaining of excessive fatigue. Also, his breath smells like raw meat/meat that is just beginning to rot. What should I do?

Gum disease. There is high probability that he is experiencing gum disease. The centers for disease control tell us that 75% of individuals over the age of 12 suffer from gum disease and this is one of the signs. It is caused by the breakdown of blood by bacteria which results in volatile sulfur compounds being produced. These can smell like rotten eggs or sewer gas.
Would recommend . A visit to the physician first for a checkup if he hasn't had one recently. A dental checkup is also advocated if he hasn't had one recently either. There could be a correlation (gi issues) or malodor could be unrelated. Hope this helps.
This means it is . Time for a medical evaluation. Can't determine the cause of his symptoms online. He will need a comprehensive medical history, physical examination & appropriate studies. Take care.
See a dentist. Sounds like he likely has an infection, may be even periodontal disease. Some medical conditions, gerd & diabetes come to mind can also be a possibility.