"They always talk about marriage, and you certainly will get married, but no date has been set," a source told Hollywood Life via Yahoo.
"There is no pressure and could happen in 2015, but could also could easily happen in 2020," the source added. "It is linked to when they want to have children because they want to do everything at once."
The singer, 22 years old, Venezuelan actor are very private about their relationship, but Lovato broke his own rule of "never [up] personal images" in November when he shared a photo of herself and Valderrama in Instagram.
"He's perfect. I miss mywilmvervalderrama," Lovato captioned photo at the moment.
See photos Demi Lovato
The couple has been dating on and off since 2010.