What is the theme in Reunions with a Ghost by Ai?

The main theme of the poem is the failure of love. The title hints at the story that unfolds, much of which is not stated explicitly but lies under the surface. "Reunions" suggests that in the relationship between this couple, there is a pattern of partings and reunions. The word "ghost" possibly refers to the man, who is only a ghost of what the woman once thought him to be (perhaps when she first fell in love with him). "Ghost" may also refer to the relationship itself, which is just a shadow of what it once was and continues in spite of the fact that, at least from the woman's point of view, there is no rationale for its continued existence.