Dido's Lament begins with a recitative ending on a V chord in the key of g minor.- I see some connections between this and the upcoming A section (very chromatic
There is a string introduction after dido ends her recitative, descending chromatically down for four measures and finally resting on the i chord where dido starts singing. This continuous bass ostinato descending line pervades the entire aria, using variations on this line too. I think think this aria would be in simple binary form.
The A section begins in g minor. There's a HC on the first phrase, and another HC on the consequent phrase ("breast"). This period is repeated again.
The B section ("remember me") has 2 periods, the first ending on a HC, the second ending on a PAC, and then the exact phrase is repeated with the same cadences.