 Lexie continues to harness romantic feelings for George , oblivious to the fact that he doesn 't see her in the same way . She prioritizes helping George study over taking part in a surgery with Mark Sloan ( Eric Dane ) , but feels betrayed when George doesn 't request that she become one of his interns after passing his exam . Finally realizing that he doesn 't feel the same way , Lexie gives up on her feelings for George and the pair 's friendship begins to fizzle out . She later begins a flirtation with Mark , and the pair begin an unlikely romantic relationship , though they are forced to keep it a secret when Meredith and Derek warn Mark away from Lexie . Lexie discovers that some of her fellow interns have secretly been performing simple procedures on each other and begins taking part . Sadie Harris ( Melissa George ) joins the society , and seeking a more daring procedure , suggests removing her appendix . Though Lexie agrees , she quickly finds herself out of her depth , resulting in Meredith and Cristina having to intervene to save Sadie 's life . Lexie and the other interns are put on probation . Derek finds Lexie distraught at the day 's events , and allows her to move into the attic at his and Meredith 's house . Mark comes clean to Derek about his relationship with Lexie , resulting in the two men getting into a fist fight . The pair continue to feud , resulting in Lexie beginning to stress eat , though they eventually reconcile . Lexie is delighted when Meredith asks her to be a bridesmaid at her and Derek 's wedding , though they eventually give the ceremony to Alex and cancer @-@ stricken Izzie Stevens ( Katherine Heigl ) . Mark decides to purchase a house and invites Lexie to move in with him , however she declines , concerned about how fast their relationship is progressing . 
