A Connecticut mother is sharing her "eight-year-long journey" to forgive her husband after he left their 15-month-old son in a hot car in July 2014, killing the toddler, in her new book, "The Gift of Ben."

That morning, July 7, at the family's Ridgefield home, started just like any other but ended in tragedy. 

Lindsey and Kyle Seitz had a routine.

"We scurried about as I rushed the girls along in their preparation for vocational Bible School. Cereal. Clothes. Brush your teeth," Lindsey Seitz recalls in her book.

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Ben Seitz wearing a "daddy's little guy" t-shirt

Ben, their only son, was a "daddy's boy" who spent that morning with Kyle while Lindsey got their two girls ready. (Lindsey Seitz)

Ben, their only son, who had big blue eyes and a full head of blond hair, was a "daddy's boy" who had spent that morning with Kyle while Lindsey got their two girls ready. Lindsey could hear Kyle blowing raspberries on Ben's belly, making the 15-month-old boy giggle. 

"You're too pretty to be a boy," Lindsey said as she looked at Ben that morning.

"I remember kissing him on the leg, and one question I have in my mind that I'll never be able to forget is did I tell him I loved him? Because … we always think we have so much more time with people. I remember that I did, but I'm not 100% sure. That's always a memory and a question that lives in the back of my mind," Lindsey told Fox News Digital.

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Lindsey drove the girls to Bible school on that "sweltering hot" day while Kyle drove Ben to day care, as was his daily routine, before he stopped to get coffee and then went into work.

Ben Seitz gets kisses on the cheeks from his sisters

"We scurried about as I rushed the girls along in their preparation for vocational Bible School. Cereal. Clothes. Brush your teeth," Lindsey Seitz recalls in her book. (Lindsey Seitz)

Lindsey recalled driving by the coffee shop and seeing his car parked there earlier than usual.

"I see your car," she texted him.

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Lindsey wonders now why she didn't text, "Wow, you dropped off Ben fast," or, "How was drop-off?" instead.

Later that day, after work, Kyle drove his son's day care center to pick up Ben. "

Where's Ben?" he asked, and the day care providers informed him that Ben had not been dropped off that morning. Kyle continued to search the rooms of the day care anyway until it dawned on him.

'The Gift of Ben' book cover

"Kyle forgot to take him to day care that morning. He passed away in the car, sitting in the parking lot of my husband’s office," Lindsey wrote in her book, "The Gift of Ben." (Lindsey Seitz)

"Kyle forgot to take him to day care that morning. He passed away in the car, sitting in the parking lot of my husband’s office," Lindsey writes in her book.

At the hospital that evening, after staff informed the Seitzes that their son "didn't make it," Lindsey wrapped her arms around her husband and immediately told him that she loved him. She could not fathom the simultaneous guilt and grief he was feeling.

Seitz told Fox News Digital she felt "unconditional love" for her husband in her heart in that moment, but forgiving him in her mind was a much longer process — a process she worked out while writing her book.

What followed over the next year included persistent media inquiries, a police investigation and questions from Department of Children and Families (DCF), which Seitz said she is grateful for in retrospect. But it made the grieving process more difficult. She was in "survival mode" for months after Ben's death.

The Seitz family

Seitz told Fox News Digital she felt "unconditional love" for her husband in her heart after their son died, but forgiving him in her mind was a much longer process. (Lindsey Seitz)

The book's message focuses more on unconditional love and forgiveness than the tragedy her family experienced more than eight years ago, Seitz said.

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"The heart and the mind are two different things," she said. "I realized, looking back, that we are 100% … partners, and we were meant to be together in this life to support each other through hard times and teach each other the lessons we needed to learn. … I don't know if it was forgiveness in the moment, but it was an overwhelming love for him."

Lindsey added that she "always knew" she would "never be able to live without" Kyle. 

Lindsey and Ben Seitz

Lindsey would "never be able to live without" Kyle. (Lindsey Seitz)

In her heart, "there was unconditional love and instantaneous forgiveness," but it took her mind nearly eight years to catch up. 

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"I started rationalizing: How could this happen? Because of my husband's actions, my son's now passed away. How can I intellectually forgive him for something like that?" she said. "And that's been an eight-year-long journey. I've forgiven him through our unconditional love, but it has been a journey of faith — an internal process that I've had to go through for many years."

Lindsey noted that she has struggled with bipolar disorder and manic depression since her early 20s, and Kyle was there to support her when she was working through ways to treat her mental illness. 

Ben Seitz plays outside

Writing and publishing "The Gift of Ben" has been a way for them to grieve together in a way they had not been able to after Ben's death. (Lindsey Seitz)

Writing and publishing "The Gift of Ben" has been a way for them to grieve together in a way they had not been able to after Ben's death.

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Lindsey now works with Kids and Car Safety, an advocacy organization that estimates more than 1,050 children have died of heatstroke in cars since 1990. A portion of the proceeds from Seitz's book will go to Kids and Car Safety and the National Alliance on Mental Illness.

She has also advocated for the passage of the Hot Cars Act of 2021, which requires new car models to alert drivers when there is weight in the backseat when they turn off their vehicles.