So it was Stewart's gut-wrenching apology to Pattinson, punctuated by her double "I love him, I love him," that shocked in its bare expression of emotion nearly as much as her admission of a fling with Rupert Sanders, the married director of Snow White and the Huntsman.
So how did Stewart, 22, go from private love to public pain? And were there any signs along the way? Here's a timeline of the key events leading up to the cheating scandal:
November 2009 – Cuddly but CoyForget the old excuse they were only together for the movie – promotion of the Twilight sequel New Moon was already done, and still Stewart and Pattinson were spotted in New York joined at the hip, then the lips.
While their castmates partied at the premiere, the pair sneaked off to hotspots like the Soho House and then Avenue before they were seen making out like high schoolers (despite the best efforts of their bodyguards to block curious eyes).
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May 2010 – A Big Fat No CommentStewart sits down for an interview, but don't even think about asking her about Pattinson. "I would never cheapen my relationships by talking about them," she tells Elle. "People say, 'Just say who you're dating. Then people will stop being so ravenous about it.' It's like, No they won't! They'll ask for specifics."
April 2011 – A Captured KissAfter looking very "couple-like" while filming Breaking Dawn in Louisiana and enjoying a date night in Vancouver, the pair are photographed kissing after the New York premiere of Pattinson's Water for Elephants.
May 2012 – Award-Caliber RomanceMore than two years into their relationship, they seem increasing less shy about expressing their love, with a PDA-filled pre-Oscar party in February followed by sharing a kiss at the May screening of Stewart's On the Road at the Cannes Film Festival.
June/July 2012 – No Outward Signs of TroubleScandal never seemed farther away. Attending a wedding for a New Jersey couple in late June, Stewart and Pattinson "stuck to each other's side all night," an attendee tells PEOPLE, as they partied with Zac Efron, Andrew Garfield and Will Koppleman.
A couple of weeks later, they turned up at Comic-Con on July 12 to promote Breaking Dawn: Part 2, with Pattinson getting silly talking about 50 Shades of Grey, saying, "I would just sit there and lick the pages." When Stewart was asked if she'd read the erotic novel in a book club with Pattinson and costar Taylor Lautner, she said simply, "That would be disgusting."
The following Thursday, July 19, they held hands as they walked to their car after a date night at Hollywood music venue Hotel Café. Then on Sunday, July 22, both collected their surfboard prizes at the Teen Choice Awards.
July 2012 – A Revealing InterviewIn early July, actress-model Liberty Ross spoke candidly about the early problems and stresses in her seven-year marriage to Rupert Sanders, who directed Snow White and the Huntsman. Moving from London to Los Angeles was surprisingly "isolating and daunting," she told YOU magazine, particularly since she was raising two children while her husband was often away for work. But she concluded by saying, "Everything feels so amazing now. We rode through the really hard times and we stuck it out."
July 24 – A Shocking RevelationSources tell PEOPLE that Stewart cheated on Pattinson with Sanders in what is described as a "fleeting moment that never should have happened." The tryst occurred recently, according to the sources, most likely between Comic-Con and the Teen Choice Awards. "Kristen is absolutely devastated," says one source.
July 25 – Admissions and ApologiesThe next morning, Stewart issues a statement to PEOPLE apologizing for the "hurt and embarrassment I've caused to those close to me and everyone this has affected." She said her "momentary indiscretion" had "jeopardized the most important thing in my life, the person I love and respect the most, Rob. I love him, I love him, I'm so sorry."
At about the same time, Sanders releases his own statement to PEOPLE, apologizing to his wife and children. "I am utterly distraught about the pain I have caused my family," he said. "My beautiful wife and heavenly children are all I have in this world. I love them with all my heart. I am praying that we can get through this together."