Hello Chiplet
I sympathise with your plight. We've been married 35 years, no one can judge how you deal with this appalling situation, except you and your partner, and you are new to each other, let alone the dreaded AD!
My MIL was less than close to her son, had thrown him out in favour of a stepfather that didn't like his long hair when he was 17, and still we have her living with us. Not everyone has a happy relationship with family. I well remember at the time ( more than 5 years ago now ) as it became obvious we had to do something as MIL was not coping on her own, that my own mother and sister tried to talk me out of it, saying we'd regret it. My mum had her own mother to live with her, not through alzheimers, and could speak from experience. However, there wasn't really much option, and no matter what you both decide, and it may take several years before you decide care is best, remember it is your decision. I hope your relationship weathers the storm.
It would do some good to realise that we don't all have close and loving family relationships.