What techniques does John Clare use in the poem "First Love" to effectively portray his emotions to the readers?

In the first two lines, the speaker claims how "struck" he was with his first love. Clare uses alliteration in the second line to give his emotion upon being struck a singing quality. The repetition of the "s" in this line also emphasizes the significant words "sudden" and "sweet." He uses two similes to illustrate the experience of being so overwhelmed that he loses all feeling and can't seem to move his body. His face "turned pale as deadly pale" and his "life and all seemed turned to clay." Similes often use "like" or "as" to make comparisons but other words such as "seem" also are used in making similes. 

In the second stanza, still overcome with emotion, he feels like he's lost his sight. Using another simile, he says that, with the loss of sight, the trees and bushes "seemed midnight at noonday." Clare then uses what is called synesthesia. This is when a writer blends or confuses senses. In this case, Clare uses sight and sound to make an evocative point that his eyes are trying to communicate the beauty of what he is seeing: 

Words from my eyes did start—

They spoke as chords do from the string, 

In the last stanza, the speaker expresses doubt with the symbolism of "winter" and "snow." If love's bed is cold, there is no warmth, no love-making, no sense of warm feelings. In the first two stanzas, he has been overwhelmed with his first love. But at this point, uncertainty arises. She "seemed" to hear his "silent voice." A silent voice is a paradox. He continues to be confused.

He doesn't get a substantial answer. One could interpret that this is a relationship that has lost its luster. But considering the other stanzas, it seems more likely that this was a brief moment of infatuation. The speaker looks upon her face, he is overwhelmed with love, he ends in confusion, and is never the same. In the last two lines, Clare personifies "heart" as it leaves its "dwelling-place" and can never return. That is to say, he has given his heart to someone and the notion that it (heart) can never return simply means that he will never be the same.