How wife in love triangle murder-suicide case discovered husband's affair: Part 3

After weeks of suspicion, Mark Gerardot said his wife Jennair told him that she had undeniable proof that he had been having an affair. Then he said she told him she had his phone cloned.
7:58 | 09/09/19

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Transcript for How wife in love triangle murder-suicide case discovered husband's affair: Part 3
New year's 2018, it's supposed to be a new beginning for mark and jennair. But trouble is just around the corner. Jennair has just moved to Delaware to join mark, who is in the midst of a quickly developing romance with his boss, Meredith. Mark was distant. He was detached. And jennair picked up on it. She suspected it had something to do with another woman. She said specifically, it's Meredith, isn't it? We had talked about Meredith before in the context of her professional decorum and I ooh-ed and aah-ed about Meredith. It wasn't too far of a leap for her to get there. And I denied it. Jennair isn't buying it. In fact she's keeping pretty close tabs on him, quizzing him about Meredith. She seems to have information she couldn't have any way of knowing and mark can't figure out how. Unbeknownst to mark his conversations with Meredith are being recorded by jennair. I've felt more joy, more excitement this fall than I ever did before. I want to see you again today. I really want to, I kind of need to -- Where are you going to be? Love you. Thanks. Love you too. Bye. She would focus on mark and Meredith and what they were doing and how she was going to catch them together. I'm counting on celebration drinks tomorrow. Every time she would get more proof, it would give her that sick feeling in her stomach. By Valentine's day, everything comes to a head. She blurts out that she has undeniable proof that mark is having an affair. At that time, jennair disclosed that she had taken my phone and had it cloned. She had hired a company to access his phone, to read his texts, to see his photos, to see a record of his calls. I finally just told her, "I'm in love with Meredith. I can't deny it anymore." And how did she react? I think she was a bit taken back that I was so bluntly honest. But to me, it was a relief to actually get it out in the open. After I admitted to having a relationship with Meredith, I said we can go to counseling. To save your marriage? We were going to go to marriage counseling. We had different, I think, intentions. Mark is getting ready to head to the marriage counselor's office and throws his coat on and he feels something in the lining of the coat. I kind of straightened the lapel and I felt this strange feeling of something that was inside the jacket. And I reached inside my pocket and I felt what I thought was an antitheft device. So I thought, "Why is there an antitheft device inside the lining of my jacket? I cut open with an x-acto blade the edge of the pocket and pulled out this device, and there was a blinking light. It was a listening device? It was a listening device. And it was sewn into the lining of your jacket? Correct. Everything begins to make sense now that mark realizes he's been bugged. Did you have a good night. This is so shocking to mark because not only has she cloned his phone, she's also bugged his actual person. She's listening in on almost everything he's doing. Even jennair's own conversations with mark are being recorded. I'm done talking about this any further. Maybe if you were truthful with me from the very beginning, I wouldn't have had to dig around like this. She told me she wanted to understand the degree to which Meredith and I were in the relationship. She was determined that there was a plan between Meredith and I, and she was trying to listen to what that plan was. She had said she was going to quit, and she was done doing it. But there's more. Mark also says jennair admits that she's written their boss at the university of Delaware about the affair and she's tracked down and told Meredith's husband. By the third counseling session, it was obvious to me that this was going in a certain direction. You wanted to end your marriage? I wanted to end the marriage. I told her, "I'm going to be filing a petition for divorce when I meet my residency requirements in may. Things are happening really quickly now. Meredith and her husband are now moving towards a divorce. And mark and Meredith are both looking for new jobs. Meredith accepted a prestigious position at Villanova university as an assistant vice president. Both she and mark are looking for new homes, around the beautiful main line suburbs in Philadelphia near her new job. Jennair on the other hand is looking ahead to what she feels is a life alone in a new city with no job and no support system. She didn't expect that at all. She just, overcome with grief that it had come to this. Everybody says it's over. I'm not there yet, I can't accept it. Jennair begins to see a divorce coach. Jennair's divorce coach is one of the few people she confides in about the rapid dissolve of her 24 year marriage. When I met with jennair, she told me mostly about the good times. Jennair really loved mark, and this was a shock to her that he was leaving. Jennair was concerned about being tossed away, and mark trading her in for a newer model, a younger model, a prettier model. You don't find me appealing. You don't find me attractive. You don't want me anymore. You don't even like me. You are miserable. She lights your fire, she makes you feel young. You're excited, it's all fresh. You're getting to know each other, and you are in love with her. She had a lot of resentment. She had a lot of anger about that. It's not unusual. She had huge fears about being left financially. I realize that this whole situation has caused you not to be able to get a job. I get that, I really do. You screwed the pooch, big time. On us, my future, your future, our future, our finances, everything. You screwed the Pooch because you made an immoral, selfish choice. According to mark, a fight erupts one night because he's found yet another listening device inside one of his jackets. I flipped over a coffee table out of anger. And I said some things that I wish I hadn't said. She was threatening to jump out the window? That was certainly the impression that I was given. Did you, at the time, did you feel like she was just trying to get attention? Yes. Or did you think she was really considering jumping out I was so scared at the moment, I didn't really know. He says he encouraged her to reach out to family and friends and a psychiatrist, which she says she did. And I thought, "I'm doing all I can do." According to mark she seemed to pull herself together and brace for the inevitable divorce. Jennair came out with a list of requirements, if you will, for how the next weeks were going to play out. That we were going to live together until may. We were going to spend as much time as possible together, going on walks, having dinners. Didn't you think that was odd? It was odd, but I'm trying to land this thing so she's in a good place. How was she acting during that time? Completely normal. Did it feel bizarre for it to seem so normal? No, I was happy that it was going to be so normal. It wasn't all sunshine and roses. There were moments of she would get upset and she would cry and she would break down. I can't watch that happen. I can't watch you have a happy life. I can't. What does that mean? We can't be friends. We cannot talk. I can't. It's too painful for me to see

This transcript has been automatically generated and may not be 100% accurate.

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