My husband has vascular dementia, the sudden declines, sometimes overnight, are a hallmark of that diagnosis. When he expresses worry and confusion, I say (brightly) "We're a team! Always have been, always will be!" I repeat that as needed, and it's true, no platitudes, no cliches. I think he is comforted by the words "We", "team", "always"

Hi Merry. My partner has Alzheimer’s Disease. We’ve only been together 21 years, & I continue to struggle with what to say & not say in moments like the one you describe. Ron is a very bright, independent guy & hates any hint that I’m taking care of him. So I try to focus on conveying respect in his ability to work things out for himself. I say, I’m sorry to hear that. Do you want to talk about it? Or, Oh hon. That must be hard. Can I help?
That approach works better for us. You must know how your husband prefers a way that you two talk that is comfortable for him. It’s tricky for me to express compassion that doesn’t sound like I am mothering him, but I’m learning from the dementia community that it is important to affirm our partner’s dignity & ability to care for themselves.
I sense that you know how to do this & will use your experience & communication skills to know what to say in your case.