My mother periodically is convinced that the man that is with her (my dad) is not HER John. That HER John has left her. She gets very upset and crying. And, of course, it's upsetting to my dad as well as they have been married for 47 years. My mother raised me not to lie and I rarely do so. Today my dad called and asked me to lie to her and tell her that I had seen dad earlier and he was running errands and would be right back. I did. And when she wakes up from her nap, she will be fine again. I feel horrible lying to her, but if it calms her, is it okay? Or am I setting myself up for her distrust of me?
I was raised, or developed my own moral/ethical compass and I wouldn't lie either...but this, you will discover as time passes, is a game of survival...for ALL. Your dad is right...It truly is okay...otherwise it increases upset and that's not good for any of you. You might start to develop a knack for it. Sort of a diversion/distraction game. The last trip my parents took a few years back to visit my sister was when we got slapped in the face with what was going on. Sister is out of state. Plane trip went fine...but on arrival we discovered how she had barely packed...and she began to whine about wanting to go home. When told the truth (going home in 9 days) she went into auto mode about oh no, she had bills to pay etc. Finally my sister just by chance said "the day after tomorrow". And that shut her up and worked...it had to of course be repeated, multiple times for the next 8 days...but it worked to appease her. If you had a good relationship prior, she will no doubt continue to trust you. Good luck...
If she is like my mother, she won't even remember the conversation the next day and it will all be behind you. but at the time, you were able to give her peace when she was experiencing fear.
I would not worry about these little confabulations setting up any kind of distrust from your mother. Her reality is now many years ago, and her denial that your dad is her husband is likely mired in that - he does not look like the man in her mind/memories. Your dad must have learned about this somewhere and it is good that he is okay with it. It's sad that she doesn't acknowledge him now, but if he wants some comfort from her, perhaps he could get some by phone - she might recognize his voice but not his current image. During one of those "errands", he could call when not in her sight and say he heard she was worried about him. He could chat for a few minutes, perhaps making both of them happy for a little while, and then say he'll be along soon, he has to finish work or errands or whatever excuse comes to mind. Because she won't remember your fibs for long, they shouldn't cause any distrust to set in.
Always keep the "return" vague, as you did (be right back, soon, in a while, etc.) Their concept of day/time is also out of whack, so try not to use dates or times. Just soon, later, etc. Be there for your dad. This is very hard on him!
An example that we recently experienced was having to decide to take my father-in-law off dialysis. He had Alzheimer's and it would have done him NO GOOD to tell him this. He was still cognitive enough to wonder why he wasn't going to dialysis, so we were told to tell him that he wasn't tolerating dialysis very well (true) and so he was having a break. He wouldn't have been able to understand at this point that he was going to die. It was difficult (as this was during the beginning of COVID and we couldn't be with him in the nursing home) but he died very peacefully.
Sadly, we have to be quite sneaky with Alzheimer's parents sometimes. It is hard on us! But try to think about things ahead of time and plan for what you will say, etc. We also learned that it is best to say TOO LITTLE about something rather than TOO MUCH. Blessings to you.
Once when she was persistent in asking, she was told dad passed. She then asked "where is he?" He was cremated and the urn is in our church mausoleum. My brother told her, "He's at the mausoleum, lying right above (name of a neighbor who passed.)" She got a laugh out of that! So there's no telling how some of this stuff registers in a damaged brain.
if you told her the truth, it might intensify her confusion and fear.
Make sure your Dad has breaks - maybe you can hire someone and spend some focused time with him. This is so painful for him.
About a week later she again asked about Cinnamon, I told her she died the past week. Another 4 to 5 days of mourning. After that whenever she asked about her dog, "everything is fine" until she completely forgot about the dog.