His wife killed his mistress in Radnor and then turned the gun on herself. Now, Mark Gerardot is finally dealing with the trauma.

Mark Gerardot lives in California now, 2,700 miles from Radnor. But his mind often drifts back to the house on Lowrys Lane, where he found his girlfriend, Meredith Chapman, dead on her kitchen floor — and not far beyond her, the bloodied body of his wife.

After nearly 30 years of marriage, Gerardot’s relationship with his wife, Jennair, had grown strained and he began an affair with Chapman, his boss at the University of Delaware. Chapman, 16 years his junior, was also in a struggling marriage.

The relationship ended both unions. And it drove Jennair Gerardot to the brink. She conducted clandestine surveillance on her husband, sewing recording devices into his clothes and tracking his phone. She feverishly followed his comings and goings and learned intimate details of the affair.

Then, on April 23, 2018, she grabbed a gun, rented a car and drove from the couple’s apartment in Wilmington to the red-brick house Chapman had rented two weeks earlier to take a new job as an assistant vice president at Villanova University. Jennair Gerardot broke into the house through its front door and lay in wait for hours. When the younger woman arrived, she shot her and then turned the gun on herself.

For 2½ years, Mark Gerardot wouldn’t discuss what happened publicly. But time in therapy slowly changed his mind, and now the 52-year-old is sharing details of his tumultuous marriage and affair and the havoc both wrought.

He has published a book, Irreparable: Three Lives. Two Deaths. One Story that Has to Be Told. And he hopes it will serve as a warning to others in similar situations.

“I always tell people to shut it down, don’t follow what happened to me,” Gerardot said in an interview from his home in San Marcos, a suburb of San Diego. “It’s not my mission per se, but it’s out there, and I want to change people’s minds before it happens again.”

For Radnor police, the crime was an open-and-shut case.

“You had a man who’s married who’s having an affair with this other woman. His wife knew that. This was a calculated attack,” Radnor Police Chief William Colarulo said at the time. “She broke into the house. She was lying in wait, and then she shot herself. There were emails and text messages indicating what she planned to do.”

The handgun used to kill both women, a Taurus Tracker .357 Magnum, was found at the scene. Jennair Gerardot bought it weeks before the crime and registered it in her name.

» READ MORE: Radnor murder-suicide sparked by love triangle, police say

Despite the book’s release, most of the people closest to the case don’t want to publicly revisit it: Colarulo and Radnor police officers involved declined to comment, as did relatives of Chapman and Jennair Gerardot.

Mark Gerardot, who has spent the last two years examining warning signs he says he was willfully oblivious to during his marriage, said he’s speaking out now, both as a form of therapy and to help others.

He recalled his wife’s paranoid behavior in the weeks leading up to the shooting.

“When this was going on, I told a divorce attorney in Newark the whole story," he said. “And she told me ‘You’ve got to get out of this; she’s going to hurt someone.'”

Gerardot met Jennair Cox in 1986, in their hometown of Fort Wayne, Ind. They became a couple four years later, a classic case of opposites attracting.

Gerardot describes himself as coming from a “strict Catholic family,” and said he didn’t have a serious girlfriend until he met his future wife. She represented everything he wasn’t, he said: She spoke her mind, she rebelled against the rules. And, slowly, he said, she began to exert control over their relationship.

Longtime friends found her behavior off-putting and told him to not marry her, he said. They pointed out that she prevented him from seeing his friends, and would stay in her bedroom whenever they had guests over.

» READ MORE: Before Radnor murder-suicide, Jennair Gerardot begged for marriage help on neighborhood app

The couple moved to Delaware in late 2017, after Gerardot accepted a position at the University of Delaware, and his wife became suspicious of her husband’s relationship with Chapman, the school’s director of marketing and his supervisor. Her instinct was right, Gerardot said: What started out as a friendly camaraderie among coworkers grew into an emotional bond, he said, with both commiserating about how unhappy they were in their marriages.

Before long, they were having an affair. But for their relationship to move out of the shadows, he said, “I knew we’d have to emotionally destroy two other people, and it hurt me. But at the same time ... I had butterflies. It felt like something I hadn’t felt in a long time.”

On New Year’s Eve, Gerardot said, he told his wife he wanted to take a break in their marriage. It was then, he said, that she began obsessively tracking his behavior.

Over the following weeks, his wife confronted him with information about private conversations he had with Chapman and details about places they’d been together. Later, she presented Meredith’s husband, Luke, with evidence of the affair. He filed for divorce days later.

Jennair Gerardot also wrote a letter to the University of Delaware detailing the relationship, and the university removed Chapman and her husband from their jobs.

Gerardot finally admitted the affair, and the two went to couple’s therapy. It soon became clear that divorce was their only option. After several emotional confrontations, Gerardot said, his wife seemed to calm down and accept that the marriage was over.

However, one day, as Gerardot was leaving his home, he felt a mysterious weight in the lapel of his jacket. When he opened the stitching, he found a small electronic recording device. And the mystery of how his wife had learned details of his time with Chapman was revealed. After another argument, she promised to stop recording him, Gerardot said.

Yet she continued her surreptitious sleuthing. She hid a GPS tracking device in the steering column of his car. And she installed software on his smartphone that “cloned” it, allowing her to see every text message and call he had made.

Sheila Brennan, a counselor who helps guide women through the logistics of divorce and was working with Jennair Gerardot, said she freely admitted she was recording her husband.

“I told her she already knew he was having an affair, and she was rubbing salt in her wounds," Brennan said. "It wasn’t healthy to track him. It was killing her.”

Brennan said Jennair Gerardot, who also worked in marketing but quit her job before moving to Delaware, worried about the financial impact of divorce and felt vulnerable and isolated in a new state where she had no friends or colleagues to turn to.

“I just kept thinking it would be better if she could just go to work so she wouldn’t be obsessed with it,” Brennan said. “It became her full-time job just to track him.”

But there was something even more ominous. Unbeknownst to her counselor and her husband, Jennair Gerardot had purchased a handgun and she had been taking lessons in how to use it.

On the day she killed Chapman and ended her own life, Jennair Gerardot cleaned the apartment she shared with her husband, leaving it “immaculate,” he said, as if guests were coming. She was supposed to meet him that night at a restaurant in Newtown Square to discuss their divorce, which they agreed to file for on May 6 — the first day they’d be eligible to apply for divorce in their new home state of Delaware.

As Gerardot waited for his wife at the bar, she texted him, saying she wanted to cancel the dinner and telling him to go home. Confused, he asked what was going on.

Then she texted him a picture of a condom taken from a trash can at Chapman’s home. And she sent him one final message.

“Bye, Mark.”

Concerned, Gerardot quickly texted Chapman. When she did not reply, he called her, and when she didn’t answer, he frantically drove to her home. There, he found the two women dead.

He was so numb from the discovery, he said, that he didn’t realize until hours later that he was initially the prime suspect: the husband of one victim, and the boyfriend of the other.

» READ MORE: Before Radnor murder-suicide, did neighbor see Jennair Gerardot spy on Meredith Chapman?

Gerardot spent months reeling from the horror of the killings. He left the Philadelphia region about a year after the shooting, unable to bear being in a place that held so many painful memories. Now, living in a sparsely decorated home near the ocean in California and taking daily walks on the beach, he hopes that telling his story — the full version, as he calls it — will bring him peace.

For him, writing the book and facing his demons was therapeutic. He knows that his actions, broadcast across the world, are not free from judgment or criticism. Part of it, he admits, is telling his side of the story.

“You make an opinion based on what you read, and nobody knew all the details, except me,” he said. “So I was going to put it all out there, and if you’re going to judge me, you’re going to do it based on all the facts, not the little bit that had been presented.”