May 16, 2012 at 2:16 PM ET
Billy Bob Thornton says he screwed up big time with Angelina Jolie.
In an interview with ABC's "Nightline" (airing Wednesday at 11:35 p.m.), the Oscar-winning actor, 56, says he realizes he "blew it" with Jolie, 36 -- who is currently engaged to Brad Pitt -- because he didn't think he was "good enough for her."
"She has one way she wanted to live her life and I had another way to live mine," Thornton reveals. "I was just too insecure."
The "Monster's Ball" star says compared to his stunning ex-wife he felt "like the Phantom of the Opera hiding in the catacombs." Harsh comments from Jolie fans didn't help. "People actually said that I didn't deserve to be with her," Thornton shares.
Adding to the strain on their marriage? Their disparate levels of fame.
"When you're in a relationship, any two celebrities or whatever, you know, I think that puts on a lot of pressure," Thornton tells Nightline. "When Angie and I got married, during that time, I was more famous than she was to start with and then she becomes this big thing, it's hard in these relationships."
Still, the actor says he deserves to shoulder the blame for his failed marriage to Jolie, with whom he says he remains "good friends."
"We had a great marriage and I chickened out because I didn't feel good enough," he admits. "That's all that happened. It was no big deal, we never hated each other."