Transcript for Why Married Women Cheat
Ever since the invention of marriage there has been infidel team. On the hit ABC show "Scandal" even the president of the united States has an affair. This season a new wrinkle his wife is having one too. Which may be art imitating life. Some studies show a dramatic spike of cheating among women in recent years. What is driving wives to stray. Could a notorious website be playing a role? Here's ABC's Rebecca Jarvis. Reporter: When women cheat it is often kiddconsidered a scandal like on the hit ABC series where even the first lady threatens to bring home wrecking to the white house. You ruined our marriage. What? You, you ruined our marriage. In movies, Diane lane played the iconic adulteress in "Unfaithful." But never has cheating been as accessible as the it is today with infidelity and anonymity a click away. What is it that drives some women to cheat? I was looking for the next high. I felt alone. Reporter: We spoke to one cheating wife, we'll call her Katherine. She asked us not to show her face and weep disguised her voice. She isn't shy about sharing her story. I went through a period where I tried to live my life like I, like I would have had I been single and 20. Reporter: Katherine and her husband were married for 14 years after major weight loss and multiple plastic surgeries she began looking for excitement outside what she kidded her own stale marriage and turned to the notorious cheater's website Ashley madison.com. I was feeling very lonely one night. I was bored. I was on my phone. In the parking lot sitting in my car. And I pulled up ashleymadison. And decided to open my first profile just to see what would happen. What it is like being a woman on Ashley Madison feeling like you are the only woman on Earth. Reporter: Its motto. Life is short. Have an affair. This man started the site ten years ago. You make $40 million a month. The second biggest dating service on the planet. Not a consider game. An enterprize of significance. Reporter: We sat down with the cup who'll rarely gives interviews. The first time he tells you about the idea what is your response? I wanted to make sure he wasn't having a mid life crisis. Reporter: He built a billion dollar business betting on infidelity. 25 million members in 37 countries. You are encouraging secrecy? I'm encouraging secrecy, not necessarily encouraging infidelity. Don't think it need encouragement. Reporter: How are you not? Long before I launched Ashley Madison there were affairs, long after I am gone. I am helping people have the more perfect affair. Katherine says she carried on affairs with men she met on line for months. Often meeting at bars, houses and traveling to other cities. I met with probably 50 or more men. Some where around 30 to 40 of those encounters led to a sexual encounter. It was addictive. It is a little like a drug. A rush. Reporter: Wendy plub knows all about the allusive allure of an affair. She says she strayed with three men during her 18 year marriage. You remember what it is like when you fell in love with your spouse. It is like that when you have an affair all over again. Reporter: It turns out she wasn't the only one who cheated. We both let the marriage down. Reporter: The veteran reporter used her ruinous marriage as the subject of "Vow" she and her husband are now divorced. I got many, many letters from women who had affairs or whose husband had affairs. This is a lot more common than I would have imagined. Reporter: Some statistics show 21% of married men have had an affair compared to 15% of married women. That number for women spiked in two decades. Up nearly 40%. Wendy says that society still judges cheating wives much more Har harshly. Even the first lady on "Scandal." Women when they cheat are viewed as having cheated on the family. When men cheat they cheat on the wife. Reporter: According to ashleymadison.com, a woman is prone to cheat at stress points in her life. Notably right before turning 40. That's what happened to Katherine. I wanted to be wanted. I wanted every man to think I have got to have her. Women cheat because they believe that they're missing something. Seems like men cheat because they want to sleep with some one else. It is less an emotional thing. In both cases the effects were devastating. Katherine's husband says she slowly began to suspect his wife's infidelity and didn't want us to show his face. The thought she was cheating on me crossed my mind. The late night meetings. Seemed unplanned. I got to be a little more suspicious. Reporter: After Katherine confessed her affair. Her husband said it left him crushed. Whatever vows we made. She said I'm breaking them right here. I said how dare she? I was furious with her. But he had his own secret. An affair started long before his wife ever turned to ashleymadison. I felt in my soul that he was seeing some one else. I really don't have a good reason why I cheated. It was just something, new, exciting. And I had no, I have no good reason why. Reporter: Though his website markets infidelity, ironically, he and his wife Amanda are happily married and completely faithful. What if your husband cheated on you? I would be devastated. Truth be told, I would be devastated. Reporter: Does it not upset you then he is encouraging that or enabling that? I don't see it as encouragement or enabling. It is going to happen. It happens regardless of the business. How would you feel if Amanda -- Devastated. If that happened. Somehow I wasn't filling what she needed in the marriage. Ashley Madison was essentially suicide. When I want to bed with the first man I met on ashleymadison I knew that, that I was dying inside. Knoll insists his business does people more good than harm. The threat of infidelity can be a marital weakup call. Reporter: You never looked yourself in the mirror and said "I am creating a platform that is enabling something that my own wife would leave me for." You see it dif Trent as a plat foreign minist minister -- platform for people to stay married. I don't think infidelity helps any marriage. People should work through their problems before it gets to infidelity. Our goal is to rip you and your marriage apart and give you the tools that you need to fix them. Reporter: Marriage counselors Jim and Elizabeth Carol run marriage retreats across the country for embattled couples forcing them to talk and even fight. Their issues out as seen on we TV marriage boot camp. The Ashley Madison site is a brilliant marketing attempt to capitalize on the basest human behavior. It plays directly into things that will destroy our culture. Reporter: Even for those couples like Katherine and her husband who have both broken their vows, the Carols say there is hope. The solution is learning how to forgive. Truly saying I will never hold this against you again. Ever. Reporter: Today Katherine has deleted her Ashley Madison profile but is estranged from her husband and kids. She says she turned to her faith for healing. It doesn't matter how bad it is, how much horrible darkness is in your life, you can always let it go and you can always be redeemed. Reporter: As her husband hold fast to his own faith, that his wife will come home. I don't believe my marriage is over. I see my wife as someone who is struggling with something internally. Someone I made a Vu ow to and promise to. Tie don't want to walk away and give up for. "Nightline," I'm Rebecca Jarvis
This transcript has been automatically generated and may not be 100% accurate.