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. Lexie is left babysitting Zola on Valentine's Day and contemplates confessing her true feelings to Mark. But 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 playdate for the kids. 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.