Madden, Pregnancy Made Richie Change Her Ways

Nicole Richie said she was finally able to break the bad "pattern" in her life, thanks to two major influences: her boyfriend, Good Charlotte lead singer Joel Madden, and her pregnancy.

Richie and Madden, a rock star and Bible reader who sports tattoos of Jesus on his arms, had not been dating long when Richie was arrested in December for driving under the influence. Madden said the incident prompted him to decide whether or not to continue the relationship.

"I said to myself, 'Well, you can walk away now and it's a great time to walk away because you can,'" Madden told Diane Sawyer. "'You have a reason. You could say, 'Nicole, it's been great, but you know, this freaked me out.' Or you could go with your gut.' And you know, my gut with Nicole has always been, she's a great woman."

Watch Part 2 of the interview on "Good Morning America" Friday and on "20/20" Friday night.

The Beverly Hills-raised adopted daughter of singer Lionel Richie said she's been dodging responsibility since she was a girl.

"It's been a pattern in my life — when I get in trouble, I try to get out of it, since I was little," said Richie, who was arrested for alleged heroin possession in February 2003 and went through rehab to kick the habit later that year.

Madden said he refused to be an enabler of anyone's addiction.

"It would be no question, because I don't have time for that, you know, at this stage in my life," said the 28-year-old singer.

Richie said that after her arrest in December, she saw herself trying to dodge responsibility once more.

"I really wasn't learning anything from that. So I kept making bad decision or mistake after mistake after mistake. And I wasn't growing. I wasn't going anywhere," she said.

Five Pregnancy Tests

In an exclusive interview with Sawyer, Richie confirmed for the first time that she is pregnant with Madden's baby.

"Yes, I am. We are. I'm almost four months," Richie told Sawyer.

Richie, 25, said she found out by taking five home pregnancy tests.

"I didn't believe it," she said. "It was my best friend and I, and we were at her house. And she was like, 'You're definitely pregnant.'"

Richie said it took a long time for the reality to sink in.

"I actually didn't even really believe it until I heard the heartbeat," she said.

Madden and Richie said they do not know the sex of the baby and are going to try to "hold out" until the birth.

Richie said the hardest part of discovering she was pregnant was the phone call she made to her dad, Lionel Richie, telling him he was going to be a grandfather.

His response, she said, was: "Now you're gonna get to experience everything that I have and everything that you've done to me. It's definitely gonna come back to you."

Richie Says She's off Drugs

Richie was arrested Dec. 12 on charges of driving under the influence after she was allegedly spotted driving the wrong way down a highway in Glendale, Calif.

Richie told Sawyer that she was driving in a new neighborhood late at night and got confused and made a wrong turn.

"I was in such shock that I just stopped the car, and in two seconds, police were there and we got off the freeway," Richie said.

The police said she admitted that she'd smoked marijuana and took the prescription painkiller Vicodin.

Richie confirmed that to Sawyer. "I had smoked marijuana that night," Richie said. "Just marijuana. I had Vicodin in my system from that day, which I take for pain."

Richie said she took Vicodin for menstrual cramps, but she never thought it would affect her driving.

When asked whether she is still taking Vicodin, Richie said, "No. I don't take anything now."

Reality Check

Richie changed her plea to guilty Friday and was sentenced to four days in jail. She has until Sept. 28 to serve the term.

She told Sawyer she pleaded guilty to the charges in order to take responsibility for her actions.

"I have a responsibility, and it's something that I did wrong, and if I could personally apologize to every single person that has lost a loved one from drunk driving I would," Richie said about her recent guilty plea. "And unfortunately, I can't, but this is my way of paying my dues and taking responsibility and being an adult."

Richie said that the reality of what she did sank in one night when she and Madden were watching a television show broadcasting images of children who had been killed in drunken-driving accidents.

She thought of her own baby then, saying that she and Madden had their first "parent moment" together.

"I owe the baby my life. I owe this baby everything and I have a responsibility now," Richie said. "Besides being responsible for myself, I'm now responsible for someone else. And I have to set the right examples. I have to really be someone that I would want my child to look up to."

Madden said he's certain he made the right decision by sticking with Richie.

"I bet on her, yeah, exactly, and that's what I did and I won," Madden said.