"I am still struggling to understand how my lover and best friend could end her life in this tragic way," the 70-year-old rocker wrote on Facebook Tuesday.
"We spent many wonderful years together and had made a great life for ourselves," he said. "She had great presence and her talent was much admired, not least by me. I have been touched by the tributes that people have paid to her, and also the personal messages of support that I have received."
"I will never forget her," he added.
The Rolling Stones also issued a statement on their website, saying they were "deeply sorry and disappointed" to postpone the tour, but hoped fans "will fully understand the reason."
Jagger had been dating the 49-year-old fashion designer since 2001.
2014: The Year in Fashion [PHOTOS]