"The Cohabitation Formulation" is the sixteenth episode of the fourth season of the American sitcom The Big Bang Theory. This episode first aired on Thursday, February 17, 2011.[1] Priya Koothrappali is back in California and she decides to start dating Leonard again. Howard is forced by Bernadette to choose between her and his mother. While Howard and Bernadette are recovering from their amorous bedroom activities, she asks Howard if he wanted to move in with her. He always ran home to help wit