"The girlfriend is not sexy and gorgeous," said Stark. "Often she is rather ordinary, not as accomplished as the wife and looks up to him and laughs at his jokes and makes the man feel like he's king of the world."
Many wives reported their husbands were "disgruntled and unhappy" at work, and figured they couldn't leave the job, but could change partners.
According to Stark's research, these runaways appear attentive and engaged before they check out, never mentioning discontent. They are typically "conflict avoiders" and described by their wives as "narcissistic."
But when they blurt out the news, their reasons are "nonsensical, exaggerated, trivial or fraudulent," she said. Oddly, she reported, most of the men leave between October and January, perhaps because their unhappiness is amplified by holiday stress.
"Quite a number of men and women have affairs, and I can understand where marriages do break down," she said, "but to leave without involving a spouse at all?"
When they jump ship, they almost always have another woman in the wings or, as in Stark's case, a longtime lover.
"It's like a parasitic relationship," she said. "He depends on his wife, and when he finds someone else to boost his self-esteem, he hops from the wife to the next partner."
When women seek help, often therapists don't understand how devastating it is, said Stark.
"Reality is distorted and the sense of betrayal is huge," she said. "If I can't trust 'George,' who I trusted with my heart and mind, who can I trust? You start to question all relationships."
When ABCNews.com did a little research of its own, two middle-aged women revealed the excruciating pain they endured after being abandoned.
Sandy and her husband from Tennessee had just celebrated the birth of their grandchild and their 30th wedding anniversary.
"He was a husband everyone thought was too good to be true, and as it turned out he was just that," she wrote.
Sandy's 55-year-old "runaway husband" had an affair with a younger co-worker, whom he moved in with and eventually married.
"I still struggle with the loss of my family as it was, and my children are broken-hearted," she said. "I have dated quite a bit, but as soon as it gets serious, I ended everything. I suppose I just do not want the commitment for fear of the pain."
Rhonda of New York state said she discovered a credit-card bill for flowers after a 30-year marriage.
"He admitted he had been having an affair for eight months," she wrote. "I had no warning whatsoever, did not suspect anything."
Her runaway husband never married the other woman and has had several girlfriends since, telling their daughter he was having a "mid-life crisis and would never get over it."
"I have never dated or gone out with anyone since," said Rhonda. "I sometimes wish that he would come back and I find it hard to let go of the past."
Stark said that in order to recover, women need to follow a path through eight "transformational stages."
The first, when the catastrophic news hits, is like a "tsunami." The erratic emotional turmoil progresses through the "thunderstorm," to the "ice storm" and later to the "sun shower" and "early spring."
It often takes two to three years to go through the process of healing and to develop a strong, new sense of self.
For Stark, who felt that her "whole world had shifted on its axis," finding others and knowing she could help them was healing.