"Their work commitments and schedules made it hard for them to continue their relationship," the source says. "Andrew is staying positive and surrounding himself with his close friends and loved ones."
On Monday, Miller posted a photo of them together on Instagram. "If you must gossip," she wrote, "at least use a cute photo. Lol love you AG."
Garfield is coming off of a busy awards season after his role as Jonathan Larson in the musical adaptation of tick, tick...BOOM! earned him an Oscar nomination, as well as a Golden Globe win for Best Actor in a Musical or Comedy.
He also made a surprise cameo in 2021's biggest blockbuster, Spider-Man: No Way Home, and is next set to star in the mini-series Under the Banner of Heaven.