The activist released an emotional message on Twitter saying she is "beyond devastated" about the loss and is asking for privacy.
"Anthony gave all of himself in everything that he did," she wrote. "His brilliant, fearless spirit touched and inspired so many, and his generosity knew no bounds. He was my love, my rock, my protector. My thoughts are with his family. I would ask that your respect their privacy and mine."
The 61-year-old culinary star was found dead in a French hotel room on June 8. The manner of death was suicide by hanging.
Argento and Bourdain have been linked since 2017. The chef was fiercely supportive of Argento's battle against sexual assault in Hollywood, and especially outspoken regarding her accusations against Harvey Weinstein.
Just five days ago, Bourdain posted a video of Argento, himself and some crew members from his hit CNN show drinking and dancing while shooting an episode of "Parts Unknown" that Argento had directed.