Payne had been spending time with his girlfriend Kate Cassidy on vacation before he died on Oct. 16 in Buenos Aires, Argentina

Liam Payne’s “erratic behavior started ramping up” when Kate Cassidy left their vacation ahead of his death on Wednesday, Oct. 16, according to a source close to the late singer’s girlfriend.

“Like you could see from the Snapchat videos, he was a different person around her,” the insider tells PEOPLE of the One Direction alum, who died at age 31 after falling from a third-floor balcony at the CasaSur Palermo Hotel in Buenos Aires, Argentina.

The source also revealed that Cassidy, 25, stood by Payne’s side during his recent “legal drama” with ex-fiancée Maya Henry.

“She had been super supportive of him through all the legal drama and very much stood by him,” the insider told PEOPLE.

In a TikTok shared Oct. 6, Henry, 23, author of the novel Looking Forward, claimed her ex — whom she doesn’t name in the book but associates with “One Direction fans” — was continuing to “blow up” her phone.

Last week, she also issued a cease-and-desist order to Payne after she claimed he repeatedly contacted her, per the Daily Mail.

Payne was first spotted with Cassidy in October 2022. While the pair largely kept their relationship quiet at the time, Cassidy shared snippets of her and Payne’s romance through red carpet photos to casual selfies.

Sources told ABC News Payne had several drugs in his body, including “pink cocaine,” at the time of his death. A partial autopsy revealed he “had multiple substances in his system” when he fell to his death.

“Pink cocaine” is a recreational drug generally including a combination of methamphetamine, ketamine, MDMA — and not necessarily cocaine — according to the National Capital Poison Center. The sources also told ABC News “an improvised aluminum pipe” was used to ingest drugs was found in Payne’s hotel room.

Per the report, the British musician’s body will remain in Argentina until the autopsy is completed.

Buenos Aires police found Liam Payne’s hotel room “in total disorder” after the singer’s death. Minutes before the balcony fall, hotel staff alerted emergency services, reporting in a 911 call that the singer had been “trashing the room,” officials said.

On Oct. 17, law enforcement investigated his room and found the prescription drug clonazepam (brand name: Klonopin), energy supplements, and other over-the-counter drugs scattered throughout the space, along with “various items broken,” including a TV. A whiskey bottle, lighter, and cellphone were later recovered from the hotel’s internal courtyard, where Payne’s body was discovered after the fall.

According to a preliminary autopsy report, the “Teardrops” singer died from multiple injuries and “internal and external” hemorrhages, the National Criminal and Correctional Prosecutor’s Office confirmed to PEOPLE.

The coroners confirmed to PEOPLE that 25 injuries in the autopsy were “compatible with those caused by a fall from a height,” explaining that “the head injuries were sufficient to cause death,” while the “internal and external hemorrhages” of the skull, thorax, abdomen and limbs contributed to Payne’s death.