The poem is about a friendship that one person mistook for romance. For most of it, the speaker seems to address someone who fell for a girl, and the sugary imagery of candy, honey and tarts stands in for her warmth. She never meant harm, but her kindness, inside jokes and friendly calls fed hope she didn't share. When she called him "like a brother," a wall went up.
The final stanzas change the picture. The question "Was I a little too sweet?" shifts the voice into the first person, and the closing line, "I'm sorry I broke your heart," suggests the speaker is the girl herself, looking back with guilt. Judging by the imagery, sweetness has turned from a pleasure into something excessive, even smothering, like sugar piled "miles high."
The mood is gentle and rueful. The rhymes and playful food images keep it light, but underneath sits a quiet regret about how easily friendliness and flirting can be confused.