<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> <P> Although initially happy in her relationship with Jackson, Lexie grows increasingly distraught and frustrated when she discovers that Mark has started dating an ophthalmologist named Julia . When she sees Mark and Julia flirting during a charity softball match, Lexie's jealousy gets the better of her and she throws a ball at Julia, injuring the latter's chest . Jackson senses that Lexie is still in love with Mark and ends their relationship . Lexie begins working under Derek's service and becomes increasingly proficient in neurosurgery, helping Derek with a set of "hopeless cases" - high risk surgeries for patients who had otherwise run out of options . During a surgery, Derek is called away on an emergency, leaving Lexie and Meredith to carry out the procedure on their own . Though Derek had instructed them to merely reduce the patient's brain tumor, Meredith allows Lexie to remove it completely, despite not being authorized by either the patient or Derek to do so . The sisters celebrate the successful surgery but Lexie is devastated when she discovers that the patient suffered severe brain damage, thus losing the ability to speak . Alex, Jackson and April move out of Meredith's house without inviting Lexie to join them, and with Derek and Meredith settling down with baby Zola, Lexie begins to feel lonely and isolated . After being left babysitting Zola on Valentine's Day, she contemplates confessing her true feelings to Mark . However, after plucking up the courage to visit his apartment, she finds Mark studying with Jackson and loses her nerve, instead claiming that she wanted to set up a play date for Zola and Sofia . When Mark confides in Derek that he and Julia have been discussing moving in together, Derek warns Lexie not to miss her chance again, resulting in her professing her love to a shell - shocked Mark, who merely thanks her for her candor . Mark later confesses to Derek that he feels the same way about Lexie, but is unsure of how to go about things . Days later, Lexie is named as part of a team of surgeons that will be sent to Boise to separate conjoined twins, along with Mark, Meredith, Derek, Cristina and Arizona Robbins (Jessica Capshaw). However, while flying to their destination, the doctors' plane crashes in the wilderness and Lexie is crushed under debris from the aircraft but manages to alert Mark and Cristina to help her . The pair try in vain to free Lexie, who realizes that she is suffering from a hemothorax and is unlikely to survive . While Cristina tries to find an oxygen tank and water to save Lexie, Mark holds Lexie's hand and professes his love for her, telling her that they will get married, have kids and live the best life together, as they are "meant to be". While fantasizing about the future that she and Mark could have had together, Lexie succumbs to her injuries and dies moments before Meredith arrives . The remaining doctors are left stranded in the woods waiting for rescue, with a devastated Meredith crying profusely and Mark refusing to let go of Lexie's hand . </P> <P> The remaining surgeons are rescued from the wilderness days later, and Lexie's body is returned to Seattle . Still devastated by Lexie's passing, Mark advises his protégé Jackson,' when you love someone, tell them', which Mark felt that he never told Lexie enough when she was alive . Mark subsequently makes a clean break with Julia, stating that he had always only truly loved Lexie . Mark is soon placed on life support due to the extensive internal injuries he sustained during the plane crash and, as determined by his will, the machines keeping him alive are eventually turned off as he showed no signs of waking after 30 days . After Mark's death, flashbacks of several moments in his life showed him being videotaped at Callie and Arizona's wedding; at the end of his congratulations speech, Mark declares that Lexie was the partner he wanted to grow old and dance with at their granddaughter's wedding . When the remaining survivors of the plane crash pool their compensation money to purchase the hospital, they agree to rename it "Grey Sloan Memorial Hospital" in tribute to Lexie and Mark . </P>

When does lexie and mark get back together