Question: why did penny and leonard break up in season 3
Answer: Leonard told Penny he loved her and took umbrage at her inability to reciprocate , which led to friction that was exploited by guest star Wil Wheaton who appeared as a fictionalized version of himself , who observed and exacerbated it in order to break them up in the middle of a bowling match Wheaton 's team was having against Leonard , Penny , Sheldon , Howard and Raj