08/01/2012 at 12:45 PM EDT
His world shattered, Robert Pattinson
turned to someone he knew he could count on: Reese Witherspoon
Immediately after learning his girlfriend of three years, Kristen Stewart
, had cheated on him
with her married Snow White and the Huntsman
director Rupert Sanders, Pattinson asked his friend and Water for Elephants
costar if he could crash at her tranquil estate
in Ojai, Calif.
Pattinson was utterly blindsided by the news – which a distraught Stewart delivered just before the story broke
July 24 on PEOPLE.com – sources tell PEOPLE in this week's cover story.
"There was no sign that either of them was unhappy," says a source close to the 26-year-old actor. "He would have done anything for her."
While the source says Pattinson has had his "heart ripped out," a Stewart insider says the Twilight
heroine, 22, is likewise devastated.
"Telling Robert was the worst thing she's ever had to do," says the insider.
For much more on Stewart's "huge mistake" – including her pleading texts and phone calls to Pattinson – and whether the actor will be able to forgive her, pick up this week's PEOPLE, on newsstands Friday