The speaker calls into an empty room, like someone stepping into a place that has been shut up for a long time. "Hello!! anybody there?" sounds cheerful, almost nervous, but the next lines turn quieter. The place is dusty, and it has been a while. Nobody has stayed.
That emptiness carries over to the speaker's feelings. People come and go, and so do emotions, and the speaker admits to feeling happy, angry, and sad all at once. It's a messy, mixed-up state that is hard to explain to anyone else, which may be part of why the speaker feels alone.
The last line pulls everything together: "an untitled book that has been forgotten." A book without a title has no name to be found by, and the speaker seems to feel unnamed and overlooked in the same way. The mood is lonely and a little sad, softened by the casual, chatty voice. The speaker sounds like they are hoping, just slightly, that someone will answer.