"She's in shock," a friend of the couple's tells PEOPLE in its new issue, on newsstands Friday. But as she's had more time to think, "She's sad – but getting angrier."
Since Bullock, 45, moved out of the Los Angeles-area home she shares with James, 40, after learning of his alleged infidelity, the actress has stayed behind closed doors as she considers whether to launch a divorce or give James a chance to mend the marriage.
Friends say that crucial to her decision is how any step will affect her relationship with James's kids from his two previous unions: Chandler, 15, Jesse Jr., 12, and Sunny, 6.
As claims of cheating continue to engulf James, many who know Bullock are puzzling over how she was so deceived.
"They're in a celebrity marriage where you really have to trust each other because the opportunities to stray are huge," explains the friend of the couple's. "He was a champ around her. He would make her feel like a million bucks."
Adds a James pal: "Bottom line: He is who he is. He's learned from things, but he will always be the same rough-around-the-edges guy."
Get a sneak peek of this week's issue – Sandra Bullock's divorce dilemma, new Jolie-Pitt twin photos and more – which is on newsstands Friday