Angelina Jolie knew that shooting "By the Sea" with Brad Pitt could potentially drown their marriage."It was our way of testing ourselves. We knew that if we could get through this, we'd come out even stronger and happier. And we did," Jolie, who wrote and directed the film, in which she and Pitt play a miserable husband and wife, told Britain's OK! magazine (via the Franchise Herald).She added, "We've always liked putting ourselves through challenges, even though it was maybe a little more dangerous for us as a couple. I don't think we want to go through it again though." But sources say Jolie and Pitt's marriage set sail long ago. According to a Hollywood Life insider, "Angie has some serious dark demons that have never entirely let go and it is still affecting her life and marriage. Her wild lifestyle when she was younger and her intense surgeries to avoid getting breast and ovarian cancer have taken a toll on her as a person and a life partner. Some of her issues force her to retreat into isolation and pull away from Brad and the kids. It is impossible to be entirely free from who she once was." Added the insider, "Angie tries to be a good mom and wife but it is difficult with her personal problems and she struggles. Brad was initially attracted to her dark side, but when she goes to this dark place she definitely pushes Brad away. It can be really hard on him. He feels he has been more than patient with Angie, but his confidence in their happiness is wearing thin." The pair's troubles apparently came to a head during their New Year's vacation in Thailand."Brad was hoping the whole family could bond, but that didn't work out either," a source recently told RadarOnline. "Despite a luxurious holiday that cost $1 million, Brad and Angie are worse off than ever. The vacation solidified the belief that their marriage is beyond repair. A divorce is definitely coming this year."