Paper Man (2009) on Netflix

Plot summary

Richard Dunn is a novelist whose work has stalled, and he still consults Captain Excellent, the imaginary superhero friend he has kept since childhood. Claire, his wife, sends him to a beach community on Long Island for the winter so that he can write. In town Richard notices Abby, a seventeen-year-old who sets a fire in a trash can, and he hires her as a weekly babysitter although he has no children. When she arrives and he admits he has no kids, she takes it in stride, and the two settle into a father-and-daughter friendship. Abby has an imaginary friend of her own, Christopher, who watches her grow close to Richard. Richard confides in Abby about his failing marriage while Captain Excellent warns him that the arrangement will only lead to bad things.