My husband has moderate dementia. I have found that trying to correct my husband's misinterpretations of what has been said or what he has seen is not a positive move for either of us. It puts him on the defensive because it just points out his deficits in communication and abilities to do what he used to be able to do without help. I have learned to ask myself "Is this a hill I want to die on?"
I will usually not correct him but rather just acknowledge what he said. Something like "oh really?" "Is that so?"If he is having difficulty with a task I say something like " these ______ are so complicated, I sometimes have trouble too. Can I help you with that?" I have found that educating myself on what the symptoms of dementia ( brain failure) and positive approaches to care have been sanity savers for me. Getting a dementia diagnosis takes time if that is what you are dealing with. Other causes should be ruled out by your physician. If possible a consult with a neurologist might be helpful to both of you. My thoughts and prayers are with you. You are not alone.