Country-music star Blake Shelton and pop star Gwen Stefani are not only a couple and mentor/judges on “The Voice,” but now they’re song-mates as well. Stefani on Tuesday tweeted a photo of the back cover of Shelton’s upcoming 12th studio album, “If I’m Honest,” with the ninth of 15 songs titled “Go Ahead And Break My Heart,” followed by the indicia “featuring Gwen Stefani.” The album is set to drop May 20.