Liam Payne’s girlfriend Kate Cassidy is still reeling from his shocking death.

On Wednesday, Kate took to Instagram to pay tribute to Liam, admitting she didn’t “even know where to begin.”

She wrote, “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. You brought so much happiness and positivity to everyone—millions of fans, your family, friends, and especially me. You are incredibly loved.”

The pair had been together for two years and were already thinking of marriage.

Kate revealed, “A few weeks ago, we sat outside on a beautiful evening manifesting our lives together. 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.'”

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Despite his death, Kate vowed to keep him in her life forever. She wrote, “Liam, I know we’ll be together forever, but not in the way we had planned. You’ll always be with me. I’ve gained a guardian angel.I will love you for the rest of my life and beyond, carrying our dreams and memories with me everywhere I go.”

Cassidy admitted that she has struggling to come to terms with his death and living life without him physically present. She noted, “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. None of this feels real, and I can’t wrap my head around this new reality of not having you here. I’m struggling to figure out how to live in a world without you by my side. Together, we got to be kids again, always finding joy in the smallest things.”

She added, “It feels like I’ve lost the best part of myself. I can’t imagine a day without your laughter and love. You brought so much light into my life.”

Payne died just two days after Cassidy left Argentina.

A source close to Kate told People magazine that Liam’s “erratic behavior started ramping up” after she flew back to Florida.

They claimed, “Like you could see from the Snapchat videos, he was a different person around her.”

Another source told The Sun U.K. that Payne’s non-immigration visa had expired and he was waiting for it to be renewed.

Before his sudden death, the source claims that the One Direction singer spoke with U.S. embassy officials, who wanted to make sure that he was clean before his visa was renewed.

Due to his drug history, the source said, “They ordered him to do medical tests, see a doctor, do bloodwork and X-rays, and see a psychiatrist and that was all done the first week.”

“Liam thought the trip would only last a few days, but because of all the tests he ended up getting stuck there,” the insider went on.

Without a renewed non-immigration visa, Liam would not have been able to fly into Miami.

The visa was scheduled to be approved on Friday, two days after Payne’s death.

Though drugs were found in his system, the source emphasized, “He was completely clean the Thursday before he died.”

They added, “On the weekend at his friend’s ranch, he was completely sober.”