If those walls could talk!

A source tells the new issue of Us Weekly (out now) that Christina Aguilera, 30, and her new boyfriend Matthew Rutler, 25, are living under the same roof as her ex Jordan Bratman -- because he refuses to move out!

"It's gotten really awkward," an Aguilera pal tells Us of life at the $11.5 million Beverly Hills mansion, where the exes look after their son Max, 3.

(After nearly five years of marriage, Aguilera filed for divorce in October 2010.)

For more details on why a distraught Aguilera sobbed openly at an L.A. nightclub, check out this week's Hot Stuff video, as explained by Senior Editor Ian Drew and comedian M. Dickson.

Also in the roundup: Justin Timberlake continues to pursue Mila Kunis, John Mayer gets heckled for being a womanizer, Marc Anthony stands up for Jennifer Lopez, and more!