Sources tell E! News that things went south on Saturday morning for the couple, who had just enjoyed a romantic dinner at West Hollywood restaurant Madeo on Thursday night followed by partying at club Voyeur.
So what went wrong?
A source close to the couple says that Munn "was shocked and upset" when she learned Pine had been seen out with blond actress Nathalie Walker Friday night at Hollywood's Roger Room.
A source says Pine reached out to Munn, who arrived in Sundance Friday, on the phone Saturday morning to apologize, but she wasn't having any of it.
"She wouldn't answer his calls and ended up texting him, telling him to leave her alone—forever," said the source.
When contacted late Saturday, Munn's rep declined to comment on the story.
E! News is reaching out to Pine for comment.
At times like these, it's important to look at The Big Picture.