this is "nightline." tonight when women cheat it is a scandal for real. why are women doing it more than ever? >> i met with probably 50 or more men. some where around 30 to 40 led to a sexual encounter. >> we are going inside a multimillion dollar business built on infidelity. plus mama bear in the heart of the alaskan wilderness. two tiny bears are about to see the light for the first time. cameras capture extraordinary footage of a mom and her cubs struggling to survive in a dangerous world. and him ellary clinton's potent 2016 campaign gets a baby bump as chelsea.

>> we have our first child arriving later this year. [ cheers and applause ] >> announces a new addition to their political dynasty. first the "nightline" top five begins right now. >> again throwing in the $1,000 fuel reward card makes dwight deals in one. >> getting a great car with 32 miles a gallon makes it two dealsen one. >> never been a better time to buy a diesel. >> during the first event, get a great deal on the jetta. and get a $1,000 pure reward card. like two deals in one. vw has the most clean diesel models of any brand. hurry in get a $1,000 fuel reward card.

good evening. 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 scand 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 pl 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 in new york. up next on "nightline." the amazing picture of a mama bear and her cubs. how far she will go to protect them. big baby news of a human variety from a member of a political dynasty. doctor. i told him i'd been feeling stuck for a long time. he said that for some people, an antidepressant alone only helps so much and suggested we add abilify (aripiprazole). he said that by taking both, some people had symptom improvement

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we humans have such mixed feelings about bears. on one hand we fear them. think of the stories about bear maulings. we adore them. nobody grows up without teddy bears. tonight you are going to got up close with the animals as never before courtesy of a fascinating new documentary. you are looking at extraordinary footage of newborn bears inside the den with their mom during their long winter's hibernation. ♪ hold on to me as we go >> and this, this is those same bears emerging for the first time into the world. what an amazing place to take your first steps. >> this new documentary called bears follows a female brown bear and her two cubs through

the first year of their life in the alaskan wilderness. and it is a treacherous year. only sky can chase him off. this mama bear is keeping a good eye. >> reporter: not only did the mama bear, named sky, have to defend her skubz, kout and amber from predators but sunny need to find enough food to sustain the family through next year's hibernation. some times this search can be comical. >> mom. never mind, i've go out. i'm fine. mom, what, what do you do if your claw gets stuck in the clam. let go! mom. it's stuck in my paw. >> you may recognize the guy that does the strovoiceover, jo. riley you may remember as reed

rothchild in boogie nights or from talladega nights. >> why you for this movie? i'm trying to figure, envision the casting session. let's get the dude from talladega nights? how did this come about? >> yeah, i mean, i'm scratching my head as much as you are. how i got this job. i think i did all right. and yeah, certainly, esteemed company. the people that have done this before. james earl jones, morgan freeman. meryl streep. pretty, pretty impressive company. >> riley brings the feisty male cub scout to life. >> scout is looking for a role model. which bear will he grow up to be? he could be an angry bear >> little male cub. i related to. super mischievous, and always thinking he could do more than

he was capable. reminded me of my stefl whself s a kid. >> go around. go around. to get amazing footage. film makers from the disney nature spent ape year in alaska's national park and preserve. at one point the filmmakers got a visit from dr. jane goodall, famous for her work with chimpanzees, disney nature's ambassador. >> were you able to get close to the bears when you were there? >> it was magic. i met the star of the movie, sky, and the two cubs. >> i met the star. >> she is the star. >> the threats facing bears these days go way beyond predators and lack of food. humans are destroying their habitat which is what can drive bears into your backyard which we have seen on countless youtube clips of late. these encounters can turn dangerous. days ago this woman in florida was maul when she stumbled upon at least five bears on her

prompt. >> i started to run. and -- and he stood up and -- just -- pushed me down. >> this is bear habitat. >> i did a story in suburban seattle with wildlife officials found a tool to discourage bears from coming into populated areas. these adorable and fearless dogs. >> there it is. wow. look at it. you can see the dogs were right on the bear. a huge outloon of a bear. three shadows of dogs on his tail. incredible. >> they also some how convinced me to dress up as a bear to help teach local kids about bear safety. as fun as it is to play bear, that awas awesome. baes signment i ha best assignment in a long time. the dangers facing the majestic pea she's are real. and the people behind this new

documentary. >> this guy looks like my dad watching tv. >> hope they can make a whole jen ration generation of kids and parents care abut this. >> i have been to national parks. usually from a distance you may have binoculars and an amazing thing to witness them. but to get this close to them, and like you do in this film, is a really special thing. i think that's only good for the world to feel more sympathy for animals. very cool to meet john c. riley. a great movie. it is called "bears" from our parent company disney in movie theaters starting tomorrow. coming of next on "nightline." the surprise today from chelsea clinton. [ male announcer ] this is the age of knowing what you're made of. why let erectile dysfunction get in your way? talk to youroctor about viagra. ask if your heart is healthy enough for sex. do not take viagra if you take nitrates for chest pain. it may cause an unsafe drop in blood pressure.

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major, personal announcement today from a woman we watched grow up in front of our eyes. chelsea clinton is pregnant. this will be a baby who attracts national interest and who could give his or her grandmother a

bump in the polls. >> reporter: the next generation of the clinton dynasty is on the way. chelsea clinton announcing today she and investment banker husband are expecting their first child. >> mark and i are very excited that we have our first child arriving later this year. but perhaps no one is more overjoyed than hillary clinton who tweeted my most exciting title yet, grandmother-to-be. her desire to add grandma to her resume has not been a secret. just last month jimmy kimmel asked her about it at the clinton global initiative. do you think you and the president will have another child? any more children? well, no. i wouldn't mind one of those grandchildren i hear so much about. >> former president bill clinton putting on the pressure too at the world economic forum three years ago. >> i would like to have a happy

wife. she won't be unless she is a grandmother. something she wants more than wanting to be president. >> chelsea married four years agoen a private ceremony. she and her husband were childhood friend who attended stanford together. today's announcement not a total surprise. last year she spoke to "glamour" magazine saying she hoped 2014 would be the year of the baby. >> i certainly feel all the better whether it is a girl or a boy. that she or he will grow up an a world full of so many strong, young, female leaders. >> reporter: for one potential leaders of the free world, perhaps a secret desire to see a grand child sliding down the white house banister, certainly it would not be the first time young children have run around the white house. even chelsea herself grew up there before our eyes. also, john, john, caroline kennedy, amy carter, jenna and barbara bush, and young american

princes and princesses, who may soon have a new member in their elite club, another clinton due this fall. for "nightline," cecelia vega, in los angeles. >> we are wishing her a healthy pregnancy. and thank you for your watching abc tonight. world news now coming up. and tune in to "gma" in the morning. we are on line 24/7 at abcnews.com. thank you for joining us. good night.