Bai's poem is about the bitter aftermath of loving someone who never loved back. The speaker opens with a flash of anger, wanting to slap the person's "perfect face," the same face they spent years smiling at. That small contrast does a lot: the beauty that once drew them in now feels like part of the insult.
Underneath the rage is real hurt. The speaker asks whether this person ever knew they were loved, and admits to dreaming of being craved in return. The repeated "years" shows how much time feels lost, and the sense of being teased, of having hope planted only for it to wither, makes the pain sharper.
The ending turns the anger inward into restraint. The speaker decides not to slap them, since the reaction would give the other person a win. The mood is raw and resentful but also self-protective, as if the speaker is trying to take back some dignity by refusing to give anything more.