"l(a" by e.e. Cummings, illustrates visually the separation that is the primary cause of loneliness.
"In a Station of the Metro" by Ezra Pound, the poem is short and alludes one to think of 'ghosts' in a metro station. He describes the people and the dreary atmosphere.
"This is Just to Say" by William Carlos Williams, explains how the speaker ate a plum and is acting (apologetic, sarcastic and smug) towards his wife.