"[Robert is] heartbroken and angry, and sources tell the magazine that he's been drinking and relying on friends to deal with the pain," says PEOPLE reporter Carlos Greer.
Stewart is also having a difficult time facing the repercussions of her affair, adds Greer.
"[Kristen is] remorseful," he says. "She's beating herself up over this."
For more details about Kristen's betrayal, how Rob found out, and the chances of their getting back together, pick up the new issue of PEOPLE, on newsstands now