I stopped colluding. If he didn’t hear me (much of the time) I refused to repeat myself. When he missed something that was happening, or a deadline, I reinforced that I’d mentioned it but he hadn’t heard me. I started sending text messages for anything g inportant, and rather than calling (shrieking) down the stairs, or across the garden.
I told family not to speak more loudly so he could hear them. I didn’t explain what others had said (anyone from guests through shop assistants). I refused to have subtitles on the few TV programmes we watch, constantly turned down the radio, Bluetooth speakers, the SatNav and so forth, so the volume was comfortable to me and mostly inaudible to him.
Took a while, but not as long as I’d feared, before he was forced to admit it was his hearing, not my lovely dulcet tones. He was nonetheless astounded that his hearing test showed severe loss in both ears!