Have you tried a tongue scraper and drinking more water

Have you checked for gingivitis

Could be anything from gingivitis to tonsil stones. Tell him how it smells, and then tell him to go to the damn dentist.

He needs to see a doctor. He could have problems in his lungs, sinuses or digestive tract that could be the source of the stank.

if you were a good girlfriend you'd not make excuses and tell him why you're not kissing him

sounds like serious halitosis or denture breath

Get him to the doctor stank breath is usually a sign of a serious health condition, bur do it soon before it's too late

Is it possible he’s got a dead tooth? My fiancé had the same problem and it turned out to be his wisdom tooth rotting

Ironically, brushing for ten minutes is likely to inflict more damage than not brushing...

This is why you should never hold in a fart. Seriously. You body absorbs the gas and re-releases it in your breath.