On Sunday, Dorsey shared a throwback photo of Josey, the five-year-old son he and the Glee star shared, and Rivera, who died in a drowning accident in July.
In the photo, the mother-son duo can be seen smiling as they prepare to eat an ice cream sundae.
“We can’t say the word happy but we’ll say thank you for being a mother & giving me this sweet amazing boy,” Dorsey captioned the photo.
The emotional tribute prompted a flood of supportive comments, with many assuring Dorsey that Rivera would be proud of him and Josey.
“May she rest in peace, you are doing such a great job with Josey, she is very proud of you,” one person wrote, while another said: “I think she’d be so proud of y’all.”
Some of Rivera’s Glee costars also shared their support, including Heather Morris, who wrote: “This broke me. I love you.”
Dorsey’s Mother’s Day post comes after he also remembered his late wife, who he was married to from 2014 to 2018, on what would have been her 34th birthday in January.
Sharing a black-and-white throwback photo of the three of them, Dorsey wrote: “Just as surreal as it is real that you’re gone. If that makes sense, but none of this still makes any sense ... 34 ... I could just hear you saying ‘Ah, I’m old AF now!’ Ha ... Rest easy old lady …”
In a separate post the same month, Dorsey celebrated the couple’s son, who he said he couldn’t be prouder of and described as “so strong, so brave, and so kind”.
“This little boy ... man ... I couldn’t be any prouder of someone. At such a young age, he’s endured more than anyone should at five years old,” he wrote.
Rivera died during a boating outing with Josey at Lake Piru in Ventura County, California. Her death was later ruled an accidental drowning.
The former couple had welcomed their son in September 2015.