Amid reports of "are they or aren't they still a couple," Gyllenhaal, 28, used the buzz word of the week – girlfriend – shortly after arriving at a Beverly Hills Hotel suite Thursday for a press conference for his new film Brothers.
"I've learned so much from the kids in my life, and somehow they just become the center of your life and the way you look at things," he told Grazia Australia, referring to his 3-year-old niece Ramona (daughter of Maggie Gyllenhaal) and possibly Witherspoon's children, Ava, 10, and Deacon, 6. "Obviously I exist in my girlfriend's world and my sister's world in a different way, but it's opened my heart and I feel much more grown up and want to be grown up as a result of it."
Regardless, he'd rather talk about his movie about a love triangle with Natalie Portman and Tobey Maguire than about his actual love life.
"As I get more famous, there is less that is just mine so I hope you understand I want to protect that as much as I can," he says. "I understand the news cycle, I really do, but as we all know news cycles come and go and I don't have to comment on them."
A source maintains to PEOPLE that Gyllenhaal and Witherspoon have split after two years together, but their reps say they are still together.