William Butler Yeats was a very prolific poet who wrote many poems in his lifetime about many different things. I think it is interesting to read the poems he wrote about love, or rather, the loss of it where he expressed a variety of emotions on his journey to understand himself and his true love.
Yeats was in desperately in love with a woman named Maud Gonne for several years, but unfortunately, she did not return his feelings. She refused to marry him, and Yeats wrote many poems detailing his feelings toward her, almost pleading to her in some, hoping she would realize how much he loved her and come back to him. In fact, he comes quite close to obsessing about the object of his affection in many of his poems.
In his 1889 poem, 'The Rose of the World', Yeats deals with the platonic ideal that was similar to Poe which believes that things are not really things, but rather a representation of themselves, like a chair, book, etc.
The first line asks:
'Who dreamed that beauty passes like a dream?'
In this poem, Yeats seems to question the ideal of beauty, and how it comes and goes in our thoughts and perceptions of people, and ourselves. He mentions "red lips" quite often in his poems, which certainly represents beauty, obviously that of a woman, but also seems to represent again the object of beauty for him, Maud Gonne. He refers to this symbol again in 'The Sorrow of Love' where:
A girl arose that had red mournful lips
And seemed the greatness of the world in tears
It is clear that the feelings Yeats had for Maud helped shape his poems and his struggle with the relationship caused him to write some of his best poems.