 Lexie feels responsible for the shooting and is unable to cope with the guilt , eventually suffering from a breakdown . She is admitted to the hospital 's psychiatric facility and is sedated for over fifty hours , with Meredith remaining by her side through it all . Alex on the other hand is less sympathetic and breaks off his and Lexie 's fling . After both realizing that they continued to have feelings for each other , Lexie and Mark resume their relationship , but their brief happiness is ruined when Lexie discovers that during their breakup , Mark had impregnated his best friend Callie Torres ( Sara Ramirez ) and she again ends their relationship . Eager to win Lexie back , Mark recruits his protégé Jackson Avery ( Jesse Williams ) to try to bring him back into Lexie 's favour , but his plan backfires when Jackson and Lexie develop romantic feelings for each other , resulting in them starting a relationship of their own . Mark is furious and tries to win Lexie back , but shortly after Callie is involved in a car accident and Lexie consoles Mark . The next episode , Lexie explains that she will go back to Mark if he continues to pursue her , despite her belief that they aren 't suited , he agrees to let her go , giving her and Jackson his blessing . 
