The Pearl Harbor star revealed they "would have ended up at each other's throats" if they continued their relationship.
"That was part of why I started drinking alcohol. I was trapped," he claimed. "I was like, 'I can't leave because of my kids, but I am not happy.'"
During the interview, Affleck also shared that their decision to part ways was mutual.
"But fundamentally, it was always underpinned with respect," the father of three explained. "I knew she was a good mom. I hope that she knew that I was a good dad. I was. I had to get sober, I knew that too, and I acknowledge that. I said, 'You're right. I've got to quit drinking.'"
Affleck's confession during the chat, however, struck Garner differently. An insider shared with OK! Magazine the 13 Going On 30 actress was not impressed by his comments.
"Jen isn't particularly happy with Ben's wording on the subject of why they divorced," the source said. "He gave an interview saying he felt 'trapped' in the marriage. Jen wouldn't have used that phrase or even opened up publicly like that. It was disrespectful."
In addition, the informant reportedly said the claims were a "slap in the face" to the mother of his child.
As RadarOnline.com previously reported, Garner isn't the only one who is not delighted by Affleck's recent statement. After learning about the situation, the actor's current girlfriend, Jennifer Lopez, is also "livid."
Sources tell us the pop star believes his partner had betrayed their agreement concerning sharing personal details with the public.
"They both agreed that they wouldn't talk about their private lives in any depth after what happened last time they were together," the insider dished. "At events, the press is told 'no questions about JLO and Ben, only questions about the film.' Now he shot off his big mouth and dragged her into it."
Affleck and Garner share three children - Samuel, 9, Seraphina, 12, and Violet, 15, after being married for ten years. Meanwhile, Lopez recently rekindled their romance after almost 17 years of calling off their engagement in 2004.
In contrast to his comments on Garner, Affleck recently gushed about his reunion with the singer.
During an interview with WSJ Magazine, he called their reconciliation is "beautiful to me," and claimed he's "very lucky in my life that I have benefited from second chances."