"There are so many things," the actress, 35, told PEOPLE in Los Angeles Wednesday night at the Grey Goose-sponsored party for Chelsea Handler's new book, Are You There, Vodka? It's Me, Chelsea.
For starters, she cited Carrey's "capacity to love and to take on something that most men would completely run away from."
McCarthy, who revealed her 5-year-old son Evan's condition nearly a year ago on The View and published a book about their experiences, Louder Than Words: A Mother's Journey in Healing Autism, said of Carrey, 46: "He could have any 20-year-old perfect girl with perfect breasts, and he stays. He has really opened his heart and his life to us. I'll forever be grateful."
Carrey and McCarthy began dating in December 2005, though the relationship did not become public until the following June.
In June 2007, McCarthy told PEOPLE that even though the two were happy together, "There will be no wedding. Goldie [Hawn] and Kurt [Russell] have it made, and that's what we can strive for."
She now also says that she doesn't see more children in their future. (Carrey, who's been married twice, has a 19-year-old daughter, Jane, with his first ex-wife.)
"I'm done," McCarthy told PEOPLE. "I got my ass kicked. All my energy and everything is on Evan to make him the best man possible."