What do i do?

So I've been dating my boyfriend for over 4 years now. We have lived together for a while. What really bothers me is the fact that he doesn't brush his teeth. Most time I refuse to kiss him and this is the main reason why. I've tried to tell him time and time again to brush them but he doesn't. He often gets angry or upset at me if I tell him his breath is bad. It honestly smells rancid.
I brush my teeth just so y'all know. I love him but this is one of my insercuritires about him. His breath is so bad. I can't kiss him at all.
What do I do?
Please help.