The 44-year-old supermodel posted a nude photo of herself sitting down with her back to the camera, leaning over to expose the bones of her back.
Alongside the fragile-looking photo, Klum wrote, "My backbone made of steel and my heart made of gold." She added the hashtag "I was not built to break."
The America's Got Talent judge confirmed that she and Vito Schnabel, an art curator and her boyfriend of three years, were pressing "pause" on their relationship.
"I believe that it is important to take time to pause and reflect," she told PEOPLE of the split.
Though Klum and Schnabel confirmed their breakup on September 25, a source said the couple was "taking time apart" earlier in the month.
"They're taking time apart right now," the insider told PEOPLE. "Things have been difficult recently, they live on opposite coasts. And it's the start of a school year and Heidi has to concentrate on the kids."
This "difficult" time came shortly after Schnabel was seen kissing another woman in London, though he claims it was an "innocent situation."
In the wake of the split news, Schnabel was arrested at Burning Man music festival on Sept. 3 for selling psychedelic shrooms. He was charges with distribution and manufacturing of a controlled substance, which is a felony.
Schnabel has reportedly pleaded not guilty to the charges. If convicted, he will face up to 5 years in prison.
As for Klum, she remains focused on the children she and ex-husband Seal share together, Henry, 12, Johan, 10, and Lou, 7, as well as her 13-year-old daughter Leni, whom she shares with ex Flavio Briatore.