Two short lines, and they hold a whole small heartbreak. The speaker looks back at a time when they believed the relationship was behind them, that the feelings had faded and life had moved on. Then comes the quiet admission: they were wrong. The "I thought" in the first line carries a lot of weight. It suggests a confident, maybe even relieved person, someone who had told themselves the story of being finished with her.
The repetition of "over her" is what makes the poem sting. The second line almost echoes the first, as if the feeling keeps returning no matter how firmly it was set aside. The plain wording and the lack of any dramatic image make it feel honest rather than performed. Nothing is explained, and the speaker doesn't dwell on it.
The mood is wistful and a little rueful, with a hint of self-mockery. It reads like someone shrugging at their own self-deception, while the ache underneath is still very much there.