Ask an Eye Doctor and Get an Answer ASAP
If the teeth are in good shape, I would suggest you ask his doctor about a chronic sinus infection, which he is at risk for, and which classically causes foul breath. Another consideration is acid reflux, which might only occur at night but can result in bad breath all day. See if you can get him a sinus CT. If infected, he needs a couple weeks of antibiotics, or more. If normal, get him on an acid blocker (e.g. prilosec, protonix) and GERD precautions (you can look these up online). This is particularly common in young men who are overweight or eat late at night.