We've got new details on the break-up between Robert Pattinson and Kristen Stewart, including the event that may have signaled the end of the star-crossed Twilight romance.

Strife began for hunky Englishman, 27, and broody beauty, 23, shortly after RPattz' return to Los Angeles following some time in New York. An insider told PEOPLE the pair "went from spending every second together, to spending more time apart at their separate houses.

"Kristen has been in a terrible mood, and it was obvious that things were not great with Rob."

The coup de grâce was when KStew was AWOL for the Remember Me star's 27th birthday celebrations May 13, a development the insider dubbed "very strange.

"He had friends over at his house, but Kristen was not part of the celebration," the insider said. "For the past few da