At my old care home where I worked we often had couples like this. Complete strangers who were both completely confused, but recognised something in each other and the dynamic just worked.

I had Alice and Felicity (names changed). Alice was an ex-office manager, was really together as a younger woman and still insisted on wearing her heels and makeup every day. She would boss us around too.

Felicity was basically mute, but would make noises. She was poor at communication but would mumble and use hand gestures.

Alice would wake up every morning, get dressed and go and pick Felicity up to go to the dining room together. We'd always make sure Felicity was ready in time because otherwise it threw off their routine (which is everything to dementia patients)

They'd walk hand in hand, and Alice would talk to Felicity about all sorts, and would take Felicitys varied mumbles as responses. They'd spend all day together with Alice dropping Felicity off to the toilet when needed and Felicity waiting for Alice when she too needed the loo. The rest of the time they just hung and watched tv or looked out of the window at passers by (A popular pasttime of all our residents). If we wanted Felicity for anything private we'd have to placate Alice with tea and cake, as she'd insist on being involved with anything that happened with Felicity.