The speaker asks for something simple and a little unusual: to borrow someone's ear. The opening line turns the old phrase "lend me an ear" into a literal request, as if listening were an object that could be handed over for a short time. The speaker doesn't want advice or comfort or even a reply. "Say not a thing" makes clear that silence from the listener is the whole point.
What drives the request is built-up pressure. The last two lines say that everything has been "kept in," never released until now. The speaker sounds like someone who has held feelings back for a long time and has finally reached the moment to speak. The repeated "for a while" keeps the request modest and polite, though the need behind it seems large.
The mood is quiet, tense and vulnerable. Short, plain lines mimic someone trying to stay calm while asking for help. The poem leaves us with the sense that being heard is a relief in itself.