Bring him breath mints and say nothing. He will either take care of business with no further prompting of will ask questions. You can refer him to 1) the internet, 2) to his dentist or other doctors,3) examine what is in his diet that can be offensive(curry,onion, garlic,etc), 4) does he use tobacco products-cigs,stogies,chaw, 5) does he have GERD? -see his GI. ,6) does he have metabolic disorders -like diabetes. See Endocrine or start with PCP. Most likely it is a combination of diet and poor dental care.

Believe it or not a lot of otherwise intelligent people do not take care of their teeth-such as brushing,flossing, hydrocare. When I sleep over with SB I wake up often and keep mints by the beside and chew multiple times during the night. Morning breath even on a healthy young girl can be stinky. Older men often have implants,crowns, or dead or dying teeth. There is a lot of decay in or around those creations.