June 25, 2012 -- In 2004, Marie Tillman became one of the most famous widows in America. Her husband, Pat Tillman, was killed in Afghanistan, after giving up a lucrative career in the NFL to join the military. His death prompted a years-long ordeal for Marie, who was thrust into the national spotlight during one of the most difficult times in her life.
Her new book, "The Letter: My Journey Through Love, Loss, & Life," chronicles the young couple's love story, and describes how Marie was able to begin living again after Pat's death.
In the first pages of the book, Marie recalls getting the visit every military family dreads. She was informed of her husband's killing in Afghanistan, nearly two years after he first enlisted with his brother.
At home that night, Marie found a letter from Pat that she refers to as a "just in case letter," to be opened only in the event of his death.
"We had written letters to each other throughout our relationship, starting when we went to different colleges," Marie told ABC News. "This one was the hardest to read, and was the one that helped me keep going after he died."
In the letter, Pat made one last request of his wife.
"Through the years I've asked a great deal of you, therefore it should surprise you little that I have another favor to ask," the letter read. "I ask that you live."
The request seemed like an impossible one at the time, she recalls in the book.
"How could he ask this? I wondered," Marie wrote. "I don't want to live. I want to die, I can't do it without you, you know that, you're the strong one, not me! I silently pleaded with him just t come back."
It took years, but she says she recognizes it now as the push she would need from her husband during her time of suffering.
"He knew what he was doing when he wrote those words," Marie wrote. "He knew that my instinct would be to give up, that sometimes I needed a gentle or not so gentle push."
In the years following Pat's death, Marie saw her husband become a sort of American icon -- a football player who left his professional career after 9/11 to serve in the army. It gradually became clear that his death wasn't exactly what the military initially said it was. He was apparently a victim of friendly fire. There was a highly-publicized Congressional investigation into the incident, drawing Marie back into the public eye three years after her husband's death. The hearings eventually revealed a military cover-up, with nobody taking responsibility.
During this time, Marie said she turned to books, from self-help to the classics, to help her cope.
"Books helped me deal with things," she told ABC News. "I sought out books about people who struggled and found themselves on the other side. Books that showed it is possible to survive."
Marie also met people through the foundation she created in her husband's memory, people who were going through similar experiences and connected with her story. She began to think she might have something that could help.
The letters she shared with her husband during their decade-long romance, and her experiences following his death became the basis of her memoir.
"I hope that when people read this book, if they are going through a hard time, they will see that it is possible to find happiness and peace," she said. "I hope it shows that you can move forward in life in a time when things are so dark and so bleak that you feel like you can't go on. I hope it gives people hope."
She has also created a website, justincaseletter.com, that showcases "just in case letters" through history, and allows people to write their own just in case letters to store in a digital vault.
Marie is remarried now and works full time with her foundation, providing support and education for veterans and their spouses.
"I was able piece my life back together and keep living like Pat asked," she told ABC News. "I hope that shows that it is possible."