How can I tell my sensitive boyfriend about his bad breath?

My boyfriend and I have been an item for 2 years. His mouth smells really bad, sometimes he wants to go down on me but I can't allow it to happen because of bacterias in that mouth. You'll ask why I'm with him if I can't tell him about something like this, he takes everything to heart and we won't speak for quite a bit. He's a yapper and loves yapping in people's faces like everyone who has a foul mouth. I told him to use one type water solution in a passing conversation and I noticed a difference but the smell is still there.

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17 h
Once I brought up a conversation about married women and girlfriends' complaining about their partners leaving skid marks on their underwear. I could see that he was beside himself, offended and uncomfortable and I haven't been the same since because it made me question everything about him. I just don't know how to bring it all up. He doesn't smell bad, he showers like your average Joe.
How can I tell my sensitive boyfriend about his bad breath?
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