Someone gets ready to go out, then waits for a person who never arrives. That's the whole situation, and the poem keeps it small and plain. The speaker dresses early, so they're ready to leave the moment the other person shows up. When the door stays closed, the speaker starts to feel foolish, as if the effort was embarrassing in itself.
The ending is where it gets interesting. The speaker decides they were forgotten, and repeats it: "I really thought you did." That extra line sounds like someone insisting on a hurt they've already settled into. Then comes the quiet final line, "I guess I was wrong." The poem never says why the person didn't come, or what the speaker was wrong about. It could mean the person didn't forget, or that the speaker shouldn't have expected so much. That gap leaves the mood uneasy and a little sad. The short, flat lines make the speaker sound tired and unsure, still caught between hope and disappointment.