I'm sonnet 116 by William Shakespear what text structure of a sonnet do these lines illustrate?

The correct answer is quatrain.

The sonnet follows a conventional structure and includes the 'usual' turn at the end that would shift the mood or meaning of the poem. This structure is frequently found in older poetry as writers tend to follow a format that offers predictability and uses a regular pattern. This pattern or rhyme scheme can be described as a-b-a-b, c-d-c-d, e-f-e-f, g-g.