 Lexie feels guilt following George 's death , having abandoned their friendship after he failed to reciprocate her romantic feelings towards him . Mark comforts her , and she eventually agrees to move into his new apartment with him . Thatcher is admitted into the hospital with liver failure stemming from his former alcoholism . When Lexie is found to not be a suitable transplant candidate , Meredith steps in and donates part of her liver , not to help Thatcher , but to spare Lexie the grief of losing her father . Mark and Lexie receive a shock when a girl named Sloan Riley shows up claiming to be Mark 's daughter , and her parentage is soon confirmed . Sloan announces her pregnancy and Mark quickly agrees to let her and the baby move in without consulting Lexie , resulting in her ending their relationship . She engages in a one @-@ night stand with Alex , but feels guilty the following day . She confesses to Mark who is furious with her , officially ending their relationship . Despite secretly suppressing her feelings for Mark , Lexie and Alex resume a casual relationship . Lexie takes part in a surgery on a patient named Alison Clark ( Caroline Williams ) and informs her husband Gary Clark ( Michael O 'Neill ) that it was a success . However , moments later Alison suffers a stroke and falls into a coma that she is deemed unlikely to wake from . As Alison had signed a DNR form , Lexie is forced to turn off the machine keeping her alive , despite Gary begging her to stop . After failing in an attempt to sue the hospital , a grief @-@ stricken Mr Clark later returns to the hospital with a gun , seeking revenge on Lexie , Derek and Richard Webber ( James Pickens , Jr . ) . After witnessing Mr Clark shoot a nurse dead , Mark shields Lexie and the pair attempt to save a critically wounded Alex . Seeking supplies , Lexie heads out into the hospital and comes face to face with Mr Clark who attempts to shoot her , but she is saved by a SWAT team member who wounds Clark at the last moment allowing her to escape . Lexie and Mark proceed to save Alex 's life . After a showdown with Richard , Gary Clark eventually commits suicide , having killed eleven people and wounding another seven , as well as causing Meredith to suffer a miscarriage . 
