Garson died Tuesday at age 57 from pancreatic cancer. He played Stanford Blatch, the best friend of Parker's Carrie Bradshaw, in the HBO series, and had already filmed scenes for the show's upcoming revival, And Just Like That…, prior to his death.
Parker, 57, paid tribute to Garson in an emotional Instagram post Friday, sharing a series of photos of them from over the years.
"It's been unbearable," she began her caption. "Sometimes silence is a statement. Of the gravity. The anguish. The magnitude of the loss of a 30 + year friendship."
She continued, "A real friendship that allowed for secrets, adventure, a shared professional family, truth, concerts, road trips, meals, late night phone calls, a mutual devotion to parenthood and all the heartaches and joy that accompany, triumphs, disappointments, fear, rage and years spent on sets (most especially Carrie's apartment) and laughing late into the night as both Stanford and Carrie and Willie and SJ."
"Willie. I will miss everything about you. And replay our last moments together. I will re-read every text from your final days and put to pen our last calls. Your absence a crater that I will fill with blessing of these memories and all the ones that are still in recesses yet to surface."
She also addressed part of her message to Garson's 21-year-old son, Nathen. "My love and deepest sympathies and condolences to you dear Nathen," the actress wrote. "You were and are the light of Willie's life and his greatest achievement was being your Papa."
Parker concluded the post by sharing Garson's last words to her: "'Great bangles all around.' Yes. Godspeed Willie Garson. RIP. X, SJ."
Earlier this week, Parker said she wasn't "ready" to comment on Garson's sudden passing, after several of her SATC costars posted their own social media tributes, including Cynthia Nixon, Kristin Davis, Kim Cattrall, Mario Cantone and Chris Noth, who shared a photo on Instagram of Garson and Parker on the HBO series' set.
"Thank you dearest Chris," Parker commented on Noth's post. "I'm not ready yet. Xxx."