Re: NO IDEA what to do
I think he has to get tested. There are many reasons for forgetfulness, Alzheimer's is only one of them. He could have had a mini stroke, some infection, or even a brain tumor.
Maybe you can schedule general checkups for the two of you together, so you don't need to point out that you suspect anything is wrong with him. But try to get word to the doctor ahead of time about what you have noticed.