Ben Affleck shares how he got better and moved on after struggles with alcohol, Part 1

The Oscar-winning actor told Diane Sawyer in an exclusive interview his dad’s addiction to alcohol taught him “how important it is for me to be sober” during the formative years for his kids.
7:55 | 02/20/20

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Transcript for Ben Affleck shares how he got better and moved on after struggles with alcohol, Part 1
That right there. That ABC news exclusive. Diane sawyer's one-on-one interview with Ben Affleck. The Oscar winning actor opening up about his struggles and how he found hope. Diane, as always, eye opening. Eye opening. Oh, thank you so much. I intervied since they lit up Hollywood with their youth and talent in "Good will hunting" and Ben was the race car talking anybody faster than ever and brimming with optimism but life is life. And today he's coming back to talk about the strength you have to find in a tough season. Oh, my gosh. Hi. Reporter: Ben Affleck strides into with his signature high octane energy. He is fast talking, funny. As we head to the gym where the junior varsity basketball team is preparing to are a playoff game. I believe in you. You'll do it. I got a very good feeling about it. Very good feeling about this game. Reporter: Affleck has a new movie coming out called "The way back." It's about a group of young basketball players who need to believe in themselves and a struggling coach who needs faith too that he can overcome addiction and reclaim his life. Which one is me? This is you. Okay. Here we go. Nice to see you again. Nice to see you again too. You look great. I think you were 27. We did our first interview. You're now 47. Like I said, you look the same. I'm -- it's quite visible. 47. You can see it. I'm not getting away with anything. A Hollywood star is ready to talk about the fault lines of addiction in his life. I've been Lew -- I got sober when I was younger, when -- in 2001, which I now look at as a sort of JV version of what really the problem is. I was sober for a couple of years and then I thought, you know, I want to just drink like a normal person and I want to have wine at dinner and so on and, you know, I was able to. I was able to for about eight years. Reporter: He says he kept a kind of balance. As he married a beloved actress. They had three children. As he grazes through the open plains. Reporter: His career as a director brought him a whole new dimension in Hollywood. Ben Affleck. Reporter: But he says he learned sooner or later your vulnerabilities can find you. I started to drink more and more and more and it was really hard for me to accept that that meant I was an alcoholic. It was like, I can just go back. I was fine before. You know, just take a break. I just need to slow down. I'm okay. You know what I mean? This isn't me. And I started to drink every day then I'd come home from work and start to drink and sit there and drink till I passed out on the Reporter: He said he wrestled depression for years and added there was rockiness in his marriage and the potent family history we didn't know. Of a little boy whose grandmother took her life amid alcohol and barbiturates. His aunt was an addict, so was his father. For me seeing my dad was -- he was drunk every day and that was just life. Then as that got worse that was really, really painful. I always said that will never be me. I'm never going to do that. I wish he had been sober during those formative years but what he taught me is how important it is for me to be sober now during these formula tiff years. Reporter: He says his mother was his rock but as his family broke apart he vowed never to repeat it. What was the hardest thing for you to be honest with yourself about? That I was going to get divorced. That -- that -- I never thought I was going to get divorced. I didn't want to get divorced. I really didn't want to be a split family with my children. And it upset me because it meant I wasn't who I thought I was and that was so painful and so disappointing. In yourself. In myself. Reporter: Two times in the last three years he went to rehab. Always worried that his drinking was affecting the children at the center of his life. I really don't want my children to pay for my sins. Or to be afraid for you. Or to be afraid for me which is one of the hard parts of being the child of an alcoholic. Do you think did what if my dad gets drunk? What if he does something stupid? What if he ends up on TMZ, you know, and done my news feed -- Did you watch the TMZ? I didn't. I didn't. I saw a little bit. I saw a little bit of it so, yes, I guess I did watch some of it although not the whole thing. I know what it looks like to be drunk. I don't need to watch any more of it. Reporter: A relapse broadcast around the world. And he says a wake-up call about the dad he is determined to be. I took the last half of the year off and just got to be dad driving to school, pick them up. Go to the swim meet, you know, that's where the parenting happens. It's in the cracks. It's in the moments where you're just taking them back from soccer and they say something profound or they talk about how they're really feeling about something and it's like, that's where you get to be the parent and that's the joy of it and that's what I don't want to Reporter: So he wanted to make the movie about the underdog team that finds a victory on the other side. One, two, three. Win. Reporter: And the coach who comes to believe that what is possible is stronger than what is past. My favorite scene in this movie and a little bit of a spoiler is where my character loses his job because it's really about consequences and you understand how desperate he is to not have to suffer those consequences and how painful that can be. Every time you say the word pain your face changes. What does it do? It -- you go somewhere. It's very painful. Divorce is very painful and alcoholism is very painful. They just are. You know, if there's something that your child is suffering, that's a level of pain that is just not easily gotten past. Not easily forgiven, not easily forgotten and it's -- it's hard. You're not going to avoid causing your kids pain, all pain, pain is part of life. I take some comfort in that. I'm doing my very, very best and I hope that that is, you know -- you know, it has to be good enough. I have to -- I don't really have a choice. I have to be the man I want to be at this point. I don't have any more room for failure of that kind. And you know he said one thing about Jennifer garner, his ex-wife, doesn't want to talk about the marriage. That was private. But he says what I want to say publicly and privately is thank you, thank you for being thoughtful, considerate, responsible and a great mom and person. So he has really begun a new path and tomorrow I'm going to bring you a little more of what he's learned about the causes underlying the alcoholism and also famous, famous glamorous cover guy is going to talk what he's learned about women as well. Oh really? Seems like of the optimism is back. Yes, yes, definitely and some of the humor. He is so funny and unpredictable as you'll see tomorrow. What is possible is greater than what has passed. That was powerful? That's where he is. Okay, morning, sunshine. The young one. Thank you. You are going to be back tomorrow and we want -- "The way back" is his movie out on March 6th and we'll see you tomorrow. See you tomorrow.

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

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