The poem opens with a question about doing something you know is bad and doing it anyway. The speaker then lines up small, almost playful examples: cutting your hair, eating a cookie, breaking a toy. Those light comparisons make the real example hit harder. It's a girl who falls in love with "you" even though everyone warned her not to.
The speaker seems to be addressing the person who hurt her, or perhaps confessing to being that person. Judging by the lines, she was "played," and the speaker admits it. There's a cold, guilty tone in the way the harm gets compared to a broken toy, as if she was something to be used up.
The mood is sad and bitter. The opening "I love you" is tender, but it returns at the end as a drunken slur, and the same words now sound like pain. She was happy for a while, the poem says, but that doesn't make the ending any easier to read.