The speaker is looking back at a relationship and clinging to the memories of it. They remember a time with someone, probably the Maria of the title, and they smile when they think of her saying "I love you." For a moment the poem feels warm and tender, almost like a happy memory being replayed.
Then the last line changes everything. The speaker admits they didn't know those words were false. The word "Yet" works like a small turn: the smile is still there in the memory, but it now sits next to the pain of the truth. The speaker still holds on, even though they know the love wasn't real.
The mood is bittersweet and quietly sad. There's no anger here, just a sense of loss and the awkward comfort of keeping something that was never what it seemed. The short, plain wording makes the hurt feel honest and unguarded.