Izzy's "Opposite Effect" is a confession from someone who believes they are toxic. The speaker says that everything they do to help or please only hurts the person they love. They call themselves "bad luck" and even "an abusive monster," and they can't understand why their partner stays. The apologies go in circles: the speaker says sorry, and the partner says sorry for making them apologize, which only deepens the speaker's guilt.
The mood is anxious, guilt-ridden and desperate. The speaker begs to be punished or thrown away, then pleads with the partner to leave before things get worse. Beneath the self-hatred is real tenderness, since the speaker clearly doesn't want to cause harm. The image of "fragile glass" captures the fear of damaging something precious. The poem ends with the nursery rhyme about Humpty Dumpty, asking whether anyone could put the partner back together once they break. It's a sad, unsettling closing line, because it suggests the speaker already feels the damage is coming.