For 10 years, A.B. Amis shepherded his wife, Frances, through the dark maze of Alzheimer's disease.

He was there through the early stages, when they laughed over Frances' locking her keys in her car, or forgetting a friend's name. But slowly the signs became unavoidable. Always the trusted copilot on their frequent road trips, Frances could no longer read a map. Once a master gardener, Frances slowly abandoned the hobby. The landscaping on their Grant, Fla., home soon deteriorated to bland, basic upkeep.

All the responsibilities Frances had maintained through nearly 60 years of marriage—paying bills, making appointments, housekeeping, cooking—fell to A.B., now 82. He accepted his new role without complaint, even as he found himself feeling less like a partner in a marriage and more like a father parenting a child. Frances needed help in the bathroom. She could get her nightgown over her head but was confounded by the arm holes. She forgot how to properly handle a fork and knife, leading to lots of spilled food. Eventually, her husband's steady hand was necessary if she was to eat.

The job of caregiver was tough, the hours long, the emotional toll enormous. A.B. watched as Frances disappeared little by little. This slow death left A.B. both immensely sad and incredibly lonely, very typical emotions for a caregiver.

"Caregiving is overwhelming, and there's no reward," says geriatric psychiatrist William Uffner, M.D., medical director for the Older Adult Program at Friends Hospital in Philadelphia. "Sometimes you wind up doing things that you would do for your 6-month- or 3 1/2-year-old child."

But a caregiver of older people doesn't get the positive feedback a child gives—growth, development, a glimpse of a future, Uffner says. Confronting a progressive series of losses is just incredibly disappointing. "And then you don't even have your husband or your wife when it gets too frustrating and you have a meltdown," he says.

A new friend

Enter Joyce, age 83, a lifelong friend of A.B. and Frances. Joyce, a widow, regularly joined A.B. and Frances for weekly lunches out. But once Frances became unable to go to restaurants, A.B.—at his son's urging—summoned the courage to ask Joyce to join him alone for lunch and, eventually, out to dinner, a little dancing, the occasional movie.

It is not at all uncommon for a caregiver to take on a "paramour," as Uffner calls it. And in many cases, entering into a new relationship can give the caregiver the strength he needs to shoulder his growing responsibilities.

"Most of the people who do those things are not abandoning their spouse," says Uffner. "It can actually be something which allows them to maintain the caretaker role in the most responsible way possible. It stops them from getting depressed, and it stops them from being too isolated."

Such an arrangement can also provide caregivers with positive feedback. They have someone who thinks they're attractive or interesting, someone to talk to about daily life, says Uffner. "Those are the things which keep us going as human beings," he says.

A different kind of arrangement

In all likelihood, this Three's Company scenario will only become more common. An estimated 5.3 million Americans have Alzheimer's disease. And as the number of people over age 65 increases, the prevalence is expected to increase by 50 percent over the next 20 years, according to the Alzheimer's Foundation.

Once A.B. started exploring his friendship with Joyce, days became less monotonous. A date on the calendar meant he had something to look forward to again. He had a companion to talk to, someone who shared his history as well as his love of corn bread and black-eyed peas. And while they never "crossed the line of decency," says A.B., he did discover how deeply he had missed being touched—holding hands, being hugged and kissed. Legally and, even possibly, morally, A.B. was cheating. But he did not feel guilty. His new relationship wasn't born of selfishness. It came from a need to survive.

"The relationship gave me hope," A.B. says. "It let me believe there was a future. By that time, I had accepted that Frances was going to die. The time was going to come, and I did not, could not, visualize myself just being alone afterwards."

When the marriage dies long before your spouse does, the result is an avalanche of emotion that can leave a caregiver depressed, depleted and isolated. Reaching out to another person for comfort is the caregiver's way of choosing to live life, says psychologist Dorree Lynn, author of Sex for Grownups.

"It is a very normal and natural progression for a caregiver to find someone to have a relationship with," says Lynn. "It's a proven fact that people who are touched, including babies, live longer. We are social creatures. We need that physical connection."

Barry Petersen can sympathize with A.B.'s journey. For him, finding a new love when his wife was stricken with Alzheimer's was his way of choosing to live. The grief he felt over his wife's disease, and the emotional toll of caregiving, brought him so low he considered suicide. But in the end, his choice to enter into a new relationship was about striking back against Alzheimer's.

"Alzheimer's took Jan," says Petersen, a correspondent for CBS News who has written a memoir, Jan's Story, about his caregiver journey. "I decided that it is not going to get both of us. By going on and by having a life, I was looking in the face of the disease and saying, 'You're not going to win twice. You took one. You won't get me. I am going to have the rest of my life.' "

Battling loneliness

A.B.'s relationship with Joyce deepened as Frances' health worsened during the last year of her life. Then in August 2009, Frances stopped taking any food or water. A.B. called hospice and did not leave his wife's side. "I held her hand those last three nights because I didn't want her to die alone in the dark," A.B. says. "We had done everything together in the past, so I figured I could help her through the dying the same way."

With his life partner gone, A.B. was filled with an unexpected onslaught of emotions: relief that her suffering, and his hard work, were over; guilt over feeling that relief; and anger at what the Alzheimer's had stolen from them both. But it was the loneliness that he found hardest to handle.

"Women have lady friends; men don't have comparable friends that they can share things with," A.B. says. "The only person that they can get close enough to, to share personal things, is a spouse or a girlfriend."

The meaning of faithful

Petersen says that, more often than not, it's women who question his choice to enter into a secondary relationship.

"Wasn't the wedding vow 'till death do us part'?" they ask. "Somebody said, 'If you really loved Jan, you would have committed a kind of emotional death. You would have given up everything,' " Petersen says. "I respect what those people say. I honor their feelings. But I personally chose a different way, and I am satisfied with what I did. For me, just for me, it's what I needed to do."

Petersen and his lady friend are committed to each other, and he says she is a full partner in his role as caregiver to Jan.

"She goes on every visit," Petersen says. "Jan loves seeing her. I see Jan, and then when we leave I am sometimes in tears, and [my lady friend] is there to help."

The need for a new relationship is not limited to husbands. Female caregivers interviewed for this article, but who were uncomfortable with having their names used, lamented most a loss of physical intimacy.

"Basic human nature is to want someone to desire, love, comfort you," says one woman, 50, who is caring for her 55-year-old husband with Alzheimer's. She has not taken on a "paramour," but often thinks about it.

"With a spouse who has Alzheimer's disease those basic needs are put on the back shelf. I don't know if turning 50 or menopause has awakened me, but I want passion back in my life." To her, passion means a man who desires her, someone to hold her, someone who knows how to kiss and caress, and someone to laugh with—all impossible to have alone.

"I know it sounds like I am selfish, and maybe I am," she says. "I just say until you have walked this journey you can't judge me."