Imagery can be of two sorts: trope and scheme. Imagery refers to the word and phrase choices a writer makes to inspire mental pictures or visions of his poem or prose that make his work live in the reader's mind.

Trope based imagery is a means of turning a sensory impression, like the feel of a cold wind, into a concrete representation in words, which then recreate the sensory impression for the reader. The means of creating trope imagery are (1) individual words (e.g., cold; brisk), (2) phrases (e.g., an icy blast), or (3) figures of speech (i.e., [a] tropes like metaphor, simile, or personification and [b] schemes like parallelism or antithesis).  The categories of trope imagery match the senses: tactile for the sense of touch, olfactory for the sense of taste, aural for the sense of hearing, visual for the sense of sight, and gustatory for the sense of taste.

Scheme imagery also refers to the creation of mental pictures or visions through word choice. However, whereas trope imagery depends on a "twist" in the meaning of the words (e.g., wind is not really a soft rustle), schematic imagery depends on the arrangement of words, for instance, "Careful men cherish things, clumsy men break things" or "Literature is full of beauty, morality, and complexity." The tools of the figures of speech in scheme imagery are (1) letters, (2) sounds, (3) word order, and (4) syntax, whereas the tool of the figures of speech in trope imagery is word meaning.

In "And Wilt Thou Leave Me Thus," Thomas Wyatt's major device for building imagery is employing figures of speech of the scheme kind. Wyatt often uses parallelism such as "grief and grame," and "wealth and woe." Wyatt also uses repetition. He repeats "And wilt thou leave me thus," and "Say nay! Say nay!" creating a parallel stanzaic structure that embraces each stanza in a repetition that is mirrored in the last line, which has internal repetition of words (diacope). In thus doing, it might be said Wyatt innovatively applies a variation of epanalepsis (repeat first at last place: "year to year") to the whole stanza. In addition, Wyatt employs scheme imagery in assonance (repetition of vowel sound: say nay, say nay; save, blame, grame). He also uses consonance (repition of consonant sounds: grief, grame; wealth, woe.)

Here's the poem with emotional imagery in bold:

And wilt thou leave me thus?
Say nay, say nay, for shame,
To save thee from the blame
Of all my grief and grame;
And wilt thou leave me thus?
Say nay, say nay!

And wilt thou leave me thus,
That hath loved thee so long
In wealth and woe among?
And is thy heart so strong
As for to leave me thus?
Say nay, say nay!

And wilt thou leave me thus,
That hath given thee my heart
Never for to depart,
Nother for pain nor smart;
And wilt thou leave me thus?
Say nay, say nay!

And wilt thou leave me thus
And have no more pity
Of him that loveth thee?
Hélas, thy cruelty!
And wilt thou leave me thus?
Say nay, say nay!

The poem is full of pathos, and its imagery is all emotional.  The main image is that of the heart; the rest are afflictions that the heart may suffer: love, pity, cruelty, pain, sorrow, wealth, woe, grief, and blame.

Also, the repeated words "nay" may serve as an image of emotional defiance to this suffering, although--frankly--it conjures up the image of a horse to me.