I'm so sorry to read this. I worked around people with dementia and it's heartbreaking. I can remember so vividly the one day a lady's husband came to visit her. He was walking right next to her, she came up to me and said, "Excuse me, sir. Do you know where my husband is?" He was such a loyal and faithful husband to her regardless of her condition. Much peace to you as you interact with your dad in the state that he is in.