The speaker looks back on a relationship that once seemed flawless, and the whole poem leans on that backward glance. Nearly every line is in the past tense, so we know from the start that something has been lost, even before the last line confirms it. The speaker insists, "Really, we were," as if still trying to convince a doubting listener, or perhaps themselves, that the love was genuine.
The short, plain sentences and the repetition of "You were mine. / I was yours" give the happiness a simple, almost childlike sweetness. The speaker says it felt "unreal, like a tale," and that phrase works two ways: it was wonderful, but it also hints that it was too good to last. Then comes the blunt final line, "Yet we fell apart," with no explanation at all. The mood is wistful and quietly sad. The speaker doesn't blame anyone or describe the breakup, which leaves us with the ache of a happy memory that now hurts.