Because my husband has the Lewy Body type Dementia he has some lucid moments (sometimes days long) but mostly he is totally confused and falling quite often. He has just started wandering at night. He also has Tardive Dyskinesia which makes it impossible for me to sleep in the same bed because of all his kicking. I have made the decision to put him in a Memory Care facility. Question is: How and when do I tell him that's what I'm going to do?
Ask for guidance from the facility. Be prepared with a plausible story such you need some time for appointments, The house has bugs to be treated, The doctor wants to do some testing, The stay is until he is better. Whatever you and he are comfortable with. To get you through the transition. The point is to make him as comfortable as possible. Others will have a different opinion. Just take them all in and know that whatever you do it will work out. It always does. You are doing the best you can and so is he. Neither of you wanted this. Not your idea. Life happens. Good luck.
Since he’s confused and not lucid much of the time, he may not understand if you tell him. If he understands in the moment, he may not remember it two minutes later. So avoid the difficulties and a grand emotional announcement, just move forward gently as you said in your title. I hope it goes well, and I admire you for making a decision that will benefit both of you.
My mom seemed to accept news better when an outside source such as the doctor or nurse told her.
Regardless of who tells him. I am glad that you have made this decision. It truly is the best thing for each of you. You can reassure him that you will visit him and oversee his care.
Wishing you peace during this difficult transitioning time in your lives.