This means that the poet spent half of his day worried about his troubles, but then he saw the beauty of nature, which put him in a good mood. To rue implies to be unhappy over something that happened or something you did because of the consequences. So, in this case, the poet was unhappy over the death of his friend but then he saw the beautiful colors in the sunset, which made him feel better. This short poem is by John Keats. He lived in England and his birthday is also called "The Day the Poet Rode Away".