First, we hear in the title that this poem is an epitaph for an old woman. As an epitaph is something that is written on a gravestone, we know that this woman is dead from the get-go.
Then, we find out that she has a family tomb, in which she is buried. Down at the bottom of the tomb, what's left of her husband's body awaits her. Since he is, at least metaphorically, dust, it's likely that he has been dead for a long time.
In sum: an old woman has been buried next to her long-dead husband, and they are finally together. The poem ends with two lines that wrap up the emotions of this event: this woman's love for life makes it even more sad that she has died. Beyond this woman and her husband, these lines apply to everyone's life and death.