Feb. 2, 2010 -- South Carolina first lady Jenny Sanford recalls how she made the "leap of faith" to marry husband Gov. Mark Sanford even though the groom refused to promise to be faithful, insisting that the clause be removed from their wedding vows.

"It bothered me to some extent, but ... we were very young, we were in love," she said in an exclusive interview with Barbara Walters to air on "20/20" Friday. "I questioned it, but I got past it ... along with other doubts that I had."

Sanford and her marriage were thrust into the national spotlight in June 2009 when her husband admitted that he had been secretly visiting his longtime lover in Argentina instead of hiking the Appalachian Trail, as he had told his staff.

Sanford learned of her husband's infidelity in January 2009, before the scandal broke. After 20 years of marriage, she moved out of the governor's mansion with the couple's four children in August and filed for divorce in December.

Following the ordeal of the last year, Sanford penned a memoir called "Staying True," a chronicle of her marriage to the governor, which will be released Friday.

Sanford, a former investment banker and Georgetown alumna, was 27 when she married Mark Sanford.

"I was a little bit surprised and maybe frankly a tiny bit disappointed that Jenny was willing to subvert herself to somebody who, frankly I didn't think was as capable as she was," Steve Rattner, her boss at the time, at the top investment bank Lazard Freres, told Walters.

After their November 1989 wedding, the newlyweds moved to Charleston, S.C., where she discovered her husband was extremely frugal -- even "cheap."

Sanford said her husband gave her less than romantic gifts for her birthday.

"He drew me a picture of a half a bike, and then for the next birthday or Christmas I got the picture of the other half a bike, and then he delivered the $25 used bike," she recalled.

For another birthday, Mark Sanford gave her a diamond necklace, which she adored, but then he took it back.

Sanford on Marriage: 'Not a Fiery Romantic Marriage'

Sanford told Walters that her husband's frugality didn't bother her.

"Once I came to understand that it really was deep-seeded in him ... it didn't bother me so much," Sanford said. "That's who he is. And isn't that one of the delicious challenges that you find in marriage? That you have to get to understand what makes somebody else tick in some respects?"

Despite his thrift, Mark Sanford was a loving, affectionate husband she said.

"We did lots of things together, everything from playing tennis to walking in the woods, to planting trees. He was very affectionate. ... We enjoyed one another's company," she said. "I would've described our marriage as not a fiery romantic marriage, necessarily, but, but a very good, steady, solid, supportive marriage."

"I thought he loved me in his own way, which is not a warm, bubbly way," she said.

Jenny Sanford Learns of Affair

One day her world came shattering down when Sanford said she found a letter in her husband's desk, which made it clear to her that he was "having a sexual relationship" with 43-year-old Argentine businesswoman Maria Belen Chapur.

"I was literally stunned," she said. "I just showed him the letter, and said, 'Can you tell me about this? Are you seeing her? What is this?' And he said, 'It's nothing, it's nothing, I'll end it.' ... And then we sat down, and he told me he was having an affair with this woman. It was incredibly painful for me."

Sanford said she gave her husband a chance to explain himself and decided to keep the affair a secret, hinging on his promises to end his relationship and change.

"My first gut instinct was to forgive him, not, not to kick him out. But, I told him immediately that I wanted to reconcile, that I would forgive him, but that it had to be over, and the marriage had to be much better. I wasn't going to go back to more of the same," she said.

Governor Begs Wife to Let Him Visit Lover

Sanford said she was in the dark about the depth of his devotion. Even after Sanford learned of her husband's unfaithfulness, she said the governor pleaded with her to stay with him, but also begged for permission to visit Chapur, whom he called his "soul mate."

"I could never have imagined this. I mean, I could never have even made this up. It never occurred to me that this person I knew, who was actually a fairly grounded person, would be asking me something so morally offensive," Sanford said. "He said, 'Why, why can't you just give me permission?' I said, 'Well, why would I give you permission? I mean, who, who gives their spouse permission to go see their lover?'"

Sanford said her husband thought giving him the OK to see Chapur was a testament to her love, which she called a string of twisted logic.

"He said to me at one point, 'Why don't you just love me.' And I said, 'Well, that's not love. I mean, love has a responsibility,'" she said.

Sanford eventually gave in and Mark Sanford flew to New York with a friend to see Chapur, promising it would be the last time he saw her.

"It was awful," she said. "It just, it ripped me up. To think that he wanted to go be with his lover is just gut-wrenching. There were days when I was a puddle, and I think I was shaking at home, in the bed, just thinking about him even being with her. And the whole two -- I think it was a two-day trip -- I mean, I was nervous the whole time."

Mark Sanford never referred to her as his "soul mate," she told Walters.

By spring 2009, Sanford began to think the damage to their marriage was beyond repair, but continued to keep their marital problems a secret, for the sake of the children and for his political career. But the world was about to find out the truth through a bizarre chain of events.

"I knew he had been having an affair. I didn't know he was in Argentina," she said.

Sanford Breaks the Mold in Face of Political Spouse's Nightmare

In the face of every political spouse's nightmare, Sanford opted not to stand by her husband's side during his June press conference when he confessed to cheating. Instead, she watched it on TV, like the rest of America.

"It was awful for me to watch my husband come back and pine about his 'soul mate,' and days spent crying in Argentina. It was awful to watch the implosion of his career that really began right there at that press conference, in many respects," she said. "It was awful to think that the world now, you know, was watching this about us and our marriage. It was awful from the political standpoint, because he really should've, should've stopped talking at a certain point. I mean, it was awful on so many levels."

The final blow to the marriage according to Sanford was a series of racy e-mails between the governor and his lover that were printed in South Carolina newspapers after the press conference.

"He talks about her tan lines and parts of her body in the emails ... nothing, nothing you ever want your children to read on the Web," she said.

Her three sons read the notes, which she said devastated them.

"Their world's been turned upside-down as well. It is something that is now a part of their lives. ... They're not happy. They're not proud. ... It just ripped me up, to see them reading these emails, and to see them have to grow up so fast."

Sanford's divorce will be final later this month, and she said she's ready to put the past behind her.

"I could go through for the rest of my life, you know, what went wrong, or where did it go wrong, and I don't know that I'll ever come up with the answer," she said. "I would say that I have acted honorably in our marriage. And I've been the best wife I can be. But now I'm looking forward to whatever comes next."