Here is a love poem stripped to its barest form. The speaker begins as if the request will be small and simple: "only one thing." That phrase sounds calm, even reasonable, and it makes us expect something modest. What arrives is the biggest thing a person can ask of someone they love: stay.
The poem's feeling sits in how it changes shape. The opening lines are steady, almost polite. Then the word "Stay" gets a line to itself, surrounded by white space, and the poem seems to run out of composure. The second line, "Please, stay," is softer and more desperate. Adding "please" suggests the speaker has nothing left to bargain with except honesty.
The mood is tender, fragile, and a little frightening. We aren't told why the speaker fears being left, and the poem doesn't need to say. The silence around those few words lets us feel the vulnerability, and the gap between what is asked and what is risked.