Kate Cassidy is “devastated and extremely heartbroken” by the sudden death of boyfriend Liam Payne, a source exclusively tells Us Weekly.

“This past week has been a nightmare for her and she is still in a state of shock,” the insider says. “It hasn’t hit her yet. Kate and Liam had a strong relationship and she feels immense guilt leaving Argentina early and leaving him alone.”

Cassidy, 25, and Payne had traveled to Buenos Aires, Argentina together earlier this month. After two weeks, the model returned home to the United States while Payne remained in Buenos Aires. (The pair started dating in 2022.)

According to the source, Payne “did not want” Cassidy to leave without him, but she was “ready to go.”

“They had been rocky in the past but they were in a good place during their vacation in Argentina, despite him wanting her to stay,” the insider tells Us, adding that Cassidy and Payne were “inseparable” most days. “Kate has seen Liam’s ups and downs over the last 2 years and knew he was struggling at times. She’s always been supportive and has stuck by him.”

News broke on October 16 that Payne fell to his death from a third-floor balcony at his hotel. The singer was 31. According to a preliminary autopsy viewed by Us, Payne died from “multiple injuries involving ‘internal and external hemorrhage’” and was in a state of semi or total unconsciousness” at the time of the fall.

Kate Cassidy and Liam Payne. Courtesy of Kate Cassidy/Instagram

Additional investigations have since concluded that Payne had multiple drugs in his system when he died. (Payne previously struggled with addiction, going to rehab in 2023.)

Cassidy has been going through a difficult time since Payne’s death, with the source telling Us that the influencer is currently “surrounded by her friends and family.”

Cassidy broke her silence about Payne’s death earlier this week.

“My heart is shattered in ways I can’t put into words. I wish you could see the huge impact you’ve had on the world, even as it feels so dark right now,” she wrote in a Wednesday, October 23, Instagram statement. “You brought so much happiness and positivity to everyone — millions of fans, your family, friends and especially me. You are so incredibly loved.”

Liam Payne and Kate Cassidy. Samir Hussein/Getty Images for Atlantis The Royal

She continued, “You are — because I can’t say were — my best friend, the love of my life and everyone you touched felt just as special as I did. Your energy was contagious, lighting up every room you walked into.”

Cassidy also noted that she and Payne had made plans for their future together.

“A few weeks ago, we sat outside on a beautiful evening manifesting our lives together,” she penned. “I keep your note close, even though you told me not to look at it. It said, ‘Me and Kate to marry within a year/engaged & together forever 444.’”

In addition to Cassidy, Payne is survived by his parents, his two older sisters and his 7-year-old son, Bear Grey, whom he shared with ex Cheryl Cole.