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 protege 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.

Is it true that do little grey and mark get back together?
yes