Almost until the last line, it seems like the speaker is watching another person: a girl with a tear on her cheek, full of love and sadness, trying to smile and failing. The details are simple, but they add up to a clear picture of someone heartbroken. The odd, painful touch is that she needs a hug from the very person who hurt her, which shows how tangled love and hurt can be.
Then the ending changes everything. The speaker wants to comfort her and say everything will be okay, but their fingers only meet the mirror. The "she" is the speaker's own reflection. That reveals the poem as a moment of self-pity and self-comfort, where the speaker wishes someone could offer the reassurance they cannot give themselves. The short, plain lines feel quiet and fragile, like words said alone in a room. The mood is tender and lonely, with a sharp sting in the final image of glass keeping the speaker apart from the comfort they want.