"Heidi just can't stay away from this loser !" a source close to the 44-year-old former supermodel told Radar.
The couple dated for three years before splitting in September after the 31-year-old art dealer was busted with psychedelic mushrooms at the Burning Man festival — and after Klum caught him cheating twice!
Despite his sleazy history, the undercover couple spent a New Year's holiday together at Nihi Sumba Resort on Sumba Island in Bali — a trip they tried to keep secret.
Though they weren't photographed together, Schnabel was spotted fishing with a Nihi Sumba employee while Klum posted photos reclining in one of the resort's hot tubs.
"Nobody was supposed to know about the reunion," revealed the insider. "Vito tried to cover it up!"
But Klum's pals had bigger concerns.
"This guy has been nothing but trouble," the source said. "No one wants him back in her life."
In late 2015, Schnabel was caught grabbing drinks with actress Dakota Johnson at New York City's White Horse Tavern — and, in 2016, spies spotted him getting up close and personal with model Dasha Zhukova.
"Heidi's got it bad for Vito," said the insider. "This is a disaster waiting to happen."
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