The couple got together soon after appearing together on The Voice, splitting with their respective spouses Miranda Lambert and Gavin Rossdale a month apart in 2015.
The two "will get married one day," says a Shelton insider, "but right now they are hyper-focused on getting pregnant."
Although Stefani is 48 and Shelton, 41, they are still hopeful to have biological children. The source said Stefani's pregnancy with her son Apollo at age 43 makes she and the country star feel hopeful about having a child together.
"They believe there is still a chance for Gwen," says the Shelton insider. "They are incredibly hopeful."
The two have been baby crazy from the start, another source told the magazine.
"Gwen and Blake started talking quickly about having a baby," they said, adding that the couple started trying for a baby last year. But so far they have ot been successful.
"Starting a family has not been easy for them," says the insider. "It's something that they really want and it's just not working out the way they wanted it to."
Although they've come up against some problems getting pregnant, the couple remains solid.
"The struggle they're facing is making them stronger," says the Shelton insider. "They are so committed to one another and protective of one another."