The speaker is congratulating someone who has taken their lover, and the congratulations are anything but kind. The poem opens as if it will be polite, but "You won" is flat and short, and then the mask slips with "the grand fucking prize." That swear word is where the anger breaks through. The "prize" is a person, and the speaker's sarcasm treats him like a trophy that was handed over.
The last lines are the most painful. "I hope you enjoy him" sounds cruel at first, but the poem slows down: "Because he meant / Everything / To me." Each word gets its own line, as if the speaker can barely get them out. Underneath the bitterness is real grief. The mood is raw and stung, a mix of sarcasm, hurt and quiet heartbreak. The poem suggests that the speaker is hiding their pain behind a joke, and that the joke stops working by the end.