An estimated 6 million Americans live with Alzheimer's disease, but a survey from UsAgainstAlzheimer's shows more than 50 percent of couples dealing with the condition have not discussed their wishes related to having another relationship. This was highlighted when the husband of lifestyle expert B. Smith revealed he was in a second relationship while he cared for her.

For CBS News' Barry Petersen, his relationship with Alzheimer's is personal. Fourteen years ago, his late wife, Jan, was diagnosed with early onset Alzheimer's. During part of that time, he also had another woman in his life. They called themselves a family of three.

The parallels to Smith, her husband Dan Gasby, and his girlfriend are uncanny. It's an all-too-common tale for couples battling Alzheimer's – one where love can be complex and unconventional.

Smith, who rose to fame as a model, lifestyle guru and restaurateur, developed early onset Alzheimer's six years ago. Today, husband Gasby is caring for his wife of 27 years.

"When B. and I realized what we're dealing with and she understood what the situation is, she said to me… 'I know what I have. I know where it's gonna take me. Tell the story. Tell the truth,'" Gasby recounted.

In January, he spoke that truth — and let cameras into his home. It's a home he shares with his wife and his girlfriend, Alex Lerner, who also has a bedroom in the house and helps with B.'s care.

"If you wanted to have a relationship, Alex, you could've chosen a lot easier paths," Petersen said.

"That's true," Lerner said with a laugh.

"Why this one?"

"I met Dan when he was pretty much at his lowest. I remember going through a time in my life where I felt that way, where I was — where I was pretty much at my lowest. And I saw the pain in his eyes, I did. And I reached out, and I thought, maybe this man just needs somebody to talk to. You know? Or as humans, sometimes we just need a hug."

"It was natural. It was organic. It was not intentional, but we fell into each other," Gasby said.

"Does she still know who you are?" Petersen asked Gasby.

"She will call me dad. She will call me her brother Gary or her brother Ron… Then she'll say Dan out of nowhere, and then I say, 'Who?' 'Dan, he's over there,'" he responded. "There may be something in her mind that says that, but then it's gone… It's like trying to drink water from a colander. No matter how much you bring it to you, there's nothing there."

It's something Petersen himself experienced with his wife, Jan. After almost 25 years together, Jan was in assisted living and could no longer remember his name. That's when Petersen met Mary Nell Wolff, who became Jan's friend.

"It broke my heart that a man who could love this woman so much couldn't remember — she could not remember who he was," Wolff said.

A year and a half after Jan passed away, Wolff and Petersen got married.

"The hardest thing, for me, is people who don't know but decide that they can judge what I'm doing," Petersen said.

"Please. I mean, we've got the 800-pound gorilla in the room. She's white, and I'm black," Gasby said, referring to Lerner and himself.

"So many people jump to conclusions and judgment, that don't even understand what Alzheimer's is, and what it does to a person, to the patient, the Alzheimer's patient, as well as the caregivers," Lerner said.

Greg O'Brien has early onset Alzheimer's. A lifelong journalist, he's written a book about being "embedded in Alzheimer's."

"I so respect what you're saying... and respect you guys and what you're going through, because it's a definition of – of – of love and… nobody understands what a caregiver goes through," O'Brien said.

He and his wife Mary Catherine raised three kids over their 42-year marriage. She's gone from wife to caregiver.

"People think that caregiving is a daytime event," Petersen said. "It's an all-night event. How do you sleep? How do you recharge? How do you rest?"

"I say one eye open and one ear open," Gasby said. Lerner agreed. "I live in a nightmare and a daymare… Everything I have to do is to mitigate her everyday irrationality — because she doesn't have that ability — maintain her dignity, and try to keep my sanity."

"This disease robs everything," O'Brien said. "It robs your brain, slowly, like a sliver every day… My brain is like an iPhone now. It's still a sophisticated device but it has a short-term battery, it pocket-dials, and it gets lost very easily."

"I try to say to people who have been critical of our relationship, you are one diagnosis away from knowing what your life will be," Wolff said.

"In our situation, even though Greg is still very functioning — we were the house that had the Super Bowl parties and the Patriots and the Red Sox, we were the house that everybody came to," Mary Catherine said. "I mean, we just did 30, 40 people summertime deck parties. He can't do that anymore. And so our social life has really narrowed down to our very, very closest friends,"

"And people run away from you," Gasby said.

"What do you want for Mary Catherine in the future?" Petersen asked O'Brien.

"I want her to be happy. I want her to marry a better person than me… And I want her to be at peace… I just don't want her to marry someone who's handsome. That's it," O'Brien said, as the group laughed.

"What you said, Greg, is what my wife said to me: 'I want you to go on' because if you truly love someone, you don't own them," Gasby said. "And what you said is the true, to me, expression of love."

"So Greg asked if we would, now that we know you, if we would watch out for you. And the answer's yes," Petersen said.

"Resoundingly yes," Gasby said.

"Thank you," Mary Catherine said, tearing up. "That was so meaningful."

The question is: When do you have "the talk" about another relationship? The answer is when you're young and healthy, because once the person you love has been diagnosed with a disease like Alzheimer's, it's already too late.