Liam Payne’s grieving girlfriend Kate Cassidy is tormented by her decision to leave her One Direction boyfriend’s side just two days before he fell to his death, a friend tells The Post.

“She did what she had to do back then,” said the friend. “She had no idea what was going to happen. I can tell you that her decision will haunt her for the rest of her life.”

The trip to Argentina was supposed to only last four days, but Payne kept asking his influencer friend to extend it. They ended up spending two weeks together before she returned to Miami.

“She wanted to be home in her own bed with her dog,” Cassidy’s friend said. “She wanted to come home.”

The friend added: “She feels bad. Everyone in her life says it’s not her fault. You can’t look after a 30-year-old adult man 24/7. But she’s not ready to hear that yet.”

Two days after leaving Argentina, Payne reportedly hired two prostitutes and embarked on a drug spree that ended in a fatal fall from his hotel balcony. The 31-year-old singer died immediately from severe internal and external injuries.

An autopsy revealed that Payne had a toxic mix of drugs in his system at the time of his death – including crack cocaine and so-called “pink cocaine,” a mix of ketamine and other drugs.

After Cassidy left Argentina and suspected her boyfriend was at a party, she encouraged him to return to Miami, the friend says. “She really tried. But he wasn’t receptive. She will forever be the villain who let him down, but that didn’t happen.”

“She was planning on being away from home for a while and he wanted to extend it indefinitely,” the source says. “She wasn’t ready for that.”

Cassidy has not commented on the online backlash against her, but on Wednesday she revealed on her Instagram that Payne had told her he wanted to ask her to marry him and that the couple had been hanging out just weeks before his death , “to manifest our life together”.

“I’m keeping your note with me, even though you told me not to look at it. It read: “Me and Kate will be married/engaged within a year and together forever 444,” she said in a message to her followers.

The 25-year-old influencer said that despite Payne’s death, they will still be “together forever” — just not “in the way we planned.”

“You will always be with me,” she wrote. “I gained a guardian angel.”