The speaker talks to a girl who hides her pain behind a smile, as the title suggests. He tells her not to fool herself: others have noticed her scars but chose not to help. He admits she never believed him when he said he cared, and he accepts that this may be fair. His tone is gentle but tinged with regret, even a little frustration.
The heart of the poem is the third stanza. All she had to do was say four small words, "I am not ok," and that would have been enough. The simplicity of the request makes the silence feel heavier. In the last stanza the speaker calls his own words "blabbering" and "moaning," as if he knows they won't reach her, because she would never talk anyway. The mood is quiet and sad, filled with helplessness. It reads like someone who wants to reach out but is unsure whether anyone, including himself, can break through her guard.