After four months of playing the field since his split from Cameron Diaz, is Justin Timberlake ready to "go steady" with Jessica Biel?

The two, who were first linked at a Golden Globe afterparty in January, recently spent several days together in the U.K., where Timberlake was touring. (They holed up in Manchester's five-star Lowry Hotel and took in a soccer match.)

And now "Justin's in love," a source close to the singer tells PEOPLE in its new issue. "She's the coolest chick ever. He wants to be with her all the time. He's ready to be serious."

Over the last few months, Timberlake, 26, and Biel, 25, have also been spotted snowboarding with pals at the Sundance Film Festival, and Biel recently attended a barbeque at Timberlake's L.A. home.

Reps for both had no comment.