They’ve been an unmarried couple for almost 20 years. Both widowed, and now in their 90s, they maintain separate residences in Florida but mostly live together in her home — an increasingly important issue because, a few years ago, she began developing memory loss.

Sometimes, she forgets to eat. She has taken some falls, too.

“His presence is helpful and supportive,” said Jenna Wells, one of her relatives and a Cornell University psychologist. “He takes her to the doctor. He takes her out to dinner.”

But he knows he will have trouble caring for her as they both age and her condition deteriorates. So he proposed to her family that the two of them move together into a continuing care retirement community, where residents can shift from independent to assisted living, then to nursing and memory care units.

If they wait too long, he points out, a facility could insist that she enter memory care directly, and he won’t be able to live there with her.

The woman’s daughter, who holds her power of attorney, opposes that plan. “She doesn’t like her mother’s gentleman friend, as we call him,” Dr. Wells said. “They’ve never gotten along. There’s mistrust about his living in her house.”

For now, with a decision on hold, the couple is managing with home care aides.

“As we see this shift, with less of a focus on marriage in older people, this is going to come up a lot,” Dr. Wells said.