It probably didn't help that Stewart appears to be wearing one of Pattinson's baseball caps during her "momentary indiscretion" with Sanders. But will the apparent betrayal be the death knell of their romance?
"There is one thing I've never understood," he told the April issue of Italian Vanity Fair. "Why people cheat. … I understand the impulse, but not how you can maintain two relationships for long."
The answer, at least for Kristen, is you can't.
"She wasn't having an affair with Rupert. It was just a fleeting moment that shouldn't have happened," an insider tells People. "She never meant to hurt anyone. She's a good person who just made a bad choice."