<P> Lexie quickly befriends George and promises not to tell anyone that he is repeating his internship after failing his intern exam . Lexie's assigned supervising resident is Meredith's best friend Cristina Yang (Sandra Oh), who doesn't take the time to learn her interns' names and thus, dubs Lexie as "Three". Although Cristina is initially rude and strict with her, Lexie eventually stands up for herself and manages to earn her mentor's respect, with Yang going so far as to acknowledge Lexie as her best student . Lexie is eager to get to know Meredith but receives a hostile response when she first introduces herself, and her later attempts to bond with her half - sister are similarly rebuffed . Lexie begins sleeping with resident Alex Karev (Justin Chambers), who discovers that Thatcher has descended into alcoholism following his wife's death and often unreasonably lashes out at Lexie . When Lexie is lectured by Meredith for not looking after Thatcher, she finally retaliates and decides to stop pursuing a relationship with Meredith . After ending her casual sexual relationship with Alex, Lexie bonds with patient Nick Hanscom (Seth Green) and is present when his exposed artery blows, causing him to suffer massive blood loss . She manages to stop the bleeding but is distraught when Nick later dies anyway . Feeling sympathy, Cristina invites Lexie to join her and Meredith in drinking and dancing, causing the sisters' relationship to begin to thaw . The following morning, Meredith goes out of her way to make Lexie breakfast, which Lexie politely eats despite being allergic to eggs, resulting in her having to be treated at the hospital . Lexie and George later agree to rent a place together, but they are only able to afford a dilapidated apartment that Lexie attempts to improve by stealing decorations and furniture from the hospital . Lexie begins to develop romantic feelings for George and secretly steals his personnel files from Chief Richard Webber's (James Pickens Jr .) office, discovering that George had only failed his intern exam by one point . She encourages George to try and convince the Chief that he deserves a second chance, to which the Chief agrees . An ecstatic George then casually plants a kiss on Lexie, completely unaware of her feelings for him . </P> <P> Lexie continues to harbor romantic feelings for an oblivious George; their relationship is a reflection of George's previous infatuation with the oblivious Meredith . She prioritizes helping George study over taking part in a rare surgery offered to her by plastics attending Mark Sloan (Eric Dane), but feels betrayed when George fails to even request that she become one of his interns after he passes his exam . Finally realizing that George doesn't feel the same way about her, Lexie gives up on her feelings for him and the pair's friendship begins to fizzle out . She soon discovers that some of her fellow interns have secretly been practicing simple procedures on each other, and begins taking part in these unauthorized operations to prove that she's "hardcore". Seeking a more daring procedure, Sadie Harris (Melissa George) later suggests that they remove her appendix . Although Lexie agrees, she quickly finds herself out of her depth and is forced to seek the aid of Meredith and Cristina to save Sadie's life, after which all of the interns in the "cabal" are put on probation . Derek finds Lexie exhausted and distraught at the day's events and allows her to move into the attic at his and Meredith's house . Lexie then begins a flirtation with Mark, and is highly impressed after watching him successfully perform a cutting - edge surgery . Later that night, she shows up at Mark's hotel room and undresses herself while repeating to him, "Teach me ." The pair grow close very quickly and enter a romantic relationship, though they are forced to keep it a secret when Derek warns Mark away from Lexie due to their large age gap and the latter being Meredith's younger sister (earning Lexie the nickname "Little Grey"). When Derek's mother (Tyne Daly) visits Seattle, Mark is initially fearful that she will disapprove of his relationship with Lexie . After meeting Lexie, however, Mrs. Shepherd tells Mark that she is exactly the kind of youthful person he should be with . When Lexie and Mark are making out in an on - call room, she accidentally gives him a penile fracture and has to seek the help of Callie Torres (Sara Ramirez) and Owen Hunt (Kevin McKidd) to treat him . Sadie then publicly takes the blame for Mark's injury to spare Lexie the burden of suffering further humiliation and guilt . Lexie later wins an intern competition organized by Izzie Stevens (Katherine Hiegl) and is congratulated by Mark . Wanting to date Mark in public, Lexie convinces him to come clean to Derek about their relationship, to which Mark agrees . But during his confession, Mark does not realize that Derek has just been devastated by the loss of a patient, and they then get into a fist fight . The two men continue to feud, resulting in Lexie beginning to stress eat until they eventually reconcile . Lexie is chosen by Mark to assist him with an extremely rare facial transplant surgery only to be judged and mocked by her peers; they believe that Mark is taking advantage of her and that she is using him . Lexie then kisses Mark in front of the other interns before stating, "They think that we're ugly but I know that we're beautiful, and we can adapt to a hostile environment ." Lexie is delighted when Meredith asks her to be a bridesmaid at her and Derek's wedding, though they ultimately give the ceremony to Alex and cancer - stricken Izzie, which Lexie attends with Mark . Lexie later asks Mark to meet her newly - sober father, which Mark initially refuses as he states that fathers have never liked him . However, Mark realizes how much he wants to build a future with Lexie, so he ends up going for dinner with her and Thatcher . Soon after, Mark decides to purchase a house and invites Lexie to move in with him only for her to decline, concerned about how fast their relationship is progressing . </P> <P> Lexie feels immense guilt following George's death, having abandoned their friendship after he failed to reciprocate her romantic feelings towards him . She is consoled by Mark and, after becoming a surgical resident, agrees to move into his new apartment with him . Lexie and the other residents grow increasingly stressed in the wake of Chief Webber's announcement that there will be a merger with Mercy West Hospital, meaning that Seattle Grace will have to layoff a large portion of its staff members . Mark encourages Lexie to relax and just try her best during this period, advising her not to worry as she deserves her job . Lexie soon finds that while she is safe from the layoffs, many of her friends have been cut from the program . To take everyone's minds off the merger, Owen takes Lexie, Mark, Derek, Meredith, and Cristina to play baseball together . Thatcher is later admitted into the hospital with liver failure stemming from his former alcoholism . When Lexie discovers that she is not a suitable transplant candidate, Meredith steps in and donates part of her liver to Thatcher to spare Lexie the grief of losing her father . Following the merger, Lexie develops a rivalry with Mercy West resident April Kepner (Sarah Drew), who desperately attempts to undermine Lexie while they are both on Derek's service . Lexie retaliates by stealing April's notebook and using its personal contents to humiliate her, though Lexie later apologizes . When a patient dies from a medical negligence mistake committed by one of the many surgeons who treated her, Webber starts a witch hunt to trace back the culprit and identify the cause of death, and Lexie is among the doctors who are questioned . It is ultimately discovered that April was the one at fault, after which Lexie and the other residents muse over the absurdity of her mistake . Despite Webber's objections, Derek recruits Lexie for his "rogue surgery" on hospital technician Isaac's (Faran Tahir) "inoperable" tumor, with Lexie acting as Derek's own caregiver during the long and exhausting procedure . Lexie is supported by Mark and, to avoid having to leave the operating room, resorts to using a diaper so that she can sufficiently hydrate herself before and during the surgery . Near the year's end, Mark and Lexie receive a shock when a pregnant teenage girl named Sloan Riley (Leven Rambin) shows up claiming to be Mark's daughter, and her parentage is soon confirmed . Mark quickly agrees to let Sloan and the baby move in permanently without consulting Lexie, resulting in her ending their relationship as she feels she is still too young to be a grandmother . An upset and drunk Lexie then engages in a one - night stand with Alex but feels guilty and confesses to Mark, who becomes furious with her despite also admitting that he had a one - night stand with Addison Montgomery (Kate Walsh). Although she secretly suppresses her feelings for Mark, Lexie and Alex assume a casual relationship that Lexie flaunts to make Mark jealous . Lexie later breaks down in front of Meredith when Alex tells her that Mark has started dating Teddy Altman (Kim Raver). After Sloan gives her baby up for adoption and leaves Seattle, however, Mark approaches Lexie and confesses his love to her . A stunned Lexie hesitantly states that Alex is now her boyfriend, to which Mark replies, "I know . I'm just saying you could have a husband ." Lexie takes part in a surgery on Alison Clark (Caroline Williams) and informs her husband Gary Clark (Michael O'Neill) that it was a success, only for Alison to suffer a stroke and fall into a coma that Derek and Webber state she is unlikely to wake from . As Alison had signed a DNR form, Lexie is forced to turn off the machines keeping her alive despite Gary begging her to stop . After failing in an attempt to sue Seattle Grace Mercy West, a grief - stricken Gary Clark later returns to the hospital with a gun, seeking revenge on Derek, Webber, and Lexie . Mark shields Lexie during the shooting and the pair attempt to save a critically wounded Alex . Lexie heads out into the evacuated hospital to search for supplies and comes face - to - face with Clark . Before Clark can shoot her, however, a SWAT team member wounds him and Lexie manages to escape . Lexie and Mark proceed to save Alex's life, during which Lexie realizes that Alex is still in love with his ex-wife Izzie, as he calls for her while delirious and on the verge of death . After having a conversation with Webber, Gary Clark eventually commits suicide, having killed eleven people and wounded another seven as well as causing Meredith to suffer a miscarriage . </P> <P> After openly acknowledging the shooting as a mass murder during a therapy session with trauma counselor Andrew Perkins (James Tupper) and the other residents, Lexie experiences a psychotic breakdown stemming from PTSD and sleep deprivation while she is treating a patient . She is admitted to the hospital's psychiatric ward, where she is sedated for over fifty hours with Meredith remaining by her side . Alex breaks off his relationship with Lexie because he cannot handle having to care for a person going through PTSD and he enjoys sleeping with women that find having been shot to be attractive . Lexie, after recovering and being cleared for surgery, confronts Alex at Cristina and Owen's wedding and knocks him down a peg by telling him that the reason he is alive is because of her . Lexie becomes irritated when others at the hospital view her as fragile and incompetent due to her breakdown and works hard to repair her image; she saves a woman from being paralyzed when no one else caught the issue . She continues to gain her confidence throughout the season and helps attending Miranda Bailey (Chandra Wilson) discover a cure for hospital fistulas . Lexie's rivalry with April intensifies when the latter begins growing closer to Meredith, but Meredith later assures Lexie that she will always be her sister . Meanwhile, Lexie and Mark continue to work together but never seem to get their timing right, with Lexie acting hostile towards Mark when he wishes to reconcile, and Mark being caught sleeping with a flavor of the day when Lexie wants to rekindle their romance . When Lexie and Mark both realize that they continue to have feelings for each other, however, they resume their relationship . Lexie nearly suffers another breakdown when the victims of a school shooting are sent to Seattle Grace Mercy West for treatment, which reminds her of her near - death experience during the shooting at the hospital . Mark comforts Lexie and the doctors ultimately manage to save all the victims of the shooting, after which Lexie tells Mark that she loves him . Lexie and Mark's happiness once again comes to a halt when she discovers that during their break - up, Mark had unintentionally impregnated Callie, and she ends their relationship once more because she is not ready for children . Thatcher is admitted to the hospital with kidney stones and Lexie is shocked to discover that he is dating a 20 - year - old girl . Concerned about Lexie's well - being and eager to win her back, Mark recruits his protégé Jackson Avery (Jesse Williams) to find out what is upsetting her . Lexie reveals to Jackson that she is frustrated with the people she cares about, specifically Mark and her father, making major life - changing decisions without considering her feelings . When Lexie overhears Mark saying that he will take care of his and Callie's child regardless of what sickness it is born with, she expresses regret for neglecting to even let Mark explain the situation before she walked away from him . However, Jackson manages to convince Lexie that nobody simply has one soulmate and the two subsequently begin dating . Mark is furious and distraught when he discovers that Jackson has entered a relationship with Lexie and desperately attempts to win her back but shortly after, Callie is involved in a severe car accident and Lexie consoles Mark . After Mark and Callie's baby is born, Mark tells Lexie that she is the only thing missing to make his life perfect . Lexie explains that she will always love Mark and will go back to him if he continues to pursue her, but she believes that they aren't suited because they have different desires . Mark then agrees to let her go, giving her and Jackson his blessing . </P>

Who does lexie from grey's anatomy end up with