"Hey hone, I noticed a change in your breath the last few weeks. I've heard that can be a symptom of infection or other illness. I think we should get it checked out."

Come from a place of medical concern. I've been dealing with this for ten years with my DH. I have to cover my nose when I talk to him, we don't kiss anymore and I can barely be near him. I asked him to see an ENT after everything else (tongue scraper etc) failed. I said it like, "I'm concerned because I know you have great oral hygeine, and you're healthy etc, so I wonder if it's an indication of something wrong." He still stinks to high hell, but hopefully you'll have better luck.

Does he take a daily medication of any kind, OP?

Some medications start to do this over time.

Mine was defensive and upset no matter how I brought it up. I tried many ways with lots of empathy. It was so bad.

Eventually he got a water pic and used an attachment on that that to flush out the tonsil stones and things were good. After that he washed out his tonsil area daily.