After three years of dating, the actors seem to have fallen victim to the perils of a long-distance relationship.
Garfield, 31, is currently shooting Martin Scorsese's new film, Silence, on location in Taiwan – and was noticeably absent from the Golden Globes and Oscars, where Stone was nominated for Best Supporting Actress.
"He's thrown himself in the project to the detriment of all else," the source says of Garfield's work on the film. "But it's too early to say the relationship is over."
"Emma understands his work anxieties – it's why she originally pulled out of Cabaret last year and only did it this year – but they're taking a break from seeing each other," the source explains. "They're both a slave to their schedules. This time last year they were privately discussing marriage."
Meanwhile, the former Superbad sweetheart, 26, has been seen spending time with her brother, Spencer, in Los Angeles after wrapping up production on her new film Aloha, starring Bradley Cooper.
Still, there is hope for the Amazing Spider-Man costars to reconcile once Garfield finishes filming in May.
"It's one of those situations where only Andrew and Emma quite know if they'll pick up where they left off or they've separated," the source says."
Another insider confirms that the split is temporary and not an official breakup.
"They are just separated for work,” the source says. "Andrew is overseas. They are both busy with their careers and have not seen each other."
The couple was last photographed together in New York City's West Village on Jan. 7. Reps for both have not commented.
With reporting by LINDA MARX