"Miley and Liam had another argument before the weekend and the engagement ring is off again," a source close to Cyrus tells PEOPLE.
Since Cyrus returned to Los Angeles after recently visiting Miami, the rift deepened between the former Disney star, 20, and the Hunger Games actor, though the couple continue to live together at Cyrus's Toluca Lake house.
This weekend, with his brother Chris, a scruffily bearded Hemsworth, looking to be in a relaxed, smiling mood, attended the City Year Spring Break event on the Sony lot in L.A – where Liam was bombarded by young female fans asking to take photos with him, which he did graciously.
Otherwise, he chatted with a few male friends and his brother, remaining at the event for about an hour.
Despite their difficulties, both Cyrus and Hemsworth agree that postponing the wedding is the "mature thing to do."
"They don't want to get married until they figure out their problems. But Miley is very worried about losing Liam. She is crazy about him," the source says.
Courtesy of Miley Cyrus
Reporting by Mia McNiece