Poets play with words and Shelley was no exception … clearly evident in the following poem …
Goodnight
Goodnight? ah no, the night is ill
Which severs those it should unite;
Let us remain together still,
Then it will be good night.
How can I call the lone night good,
Though thy sweet wishes wing its flight?
Be it not said, thought, understood;
Then it will be good night.
To hearts which near each other move
From evening close to morning light
The night is good; because my love,
They never say goodnight.
P. B. Shelley (1792 – 1822)
It is essential to have the words before you to understand this poem. There is a difference between good night and goodnight!
In stanza one the night will not be good if ‘you’ are not by my side, implying a close relationship with someone.
In stanza two the night will not be good if there is thought or an understanding of a separation; even though the person has sweet wishes.
And in stanza three, for those that are in total commune with their soulmates, there is no need to say goodnight – no break in the spiritual connection that Shelley associates with the word goodnight. The night will always be good.
The philosophy and poetry of P. B. Shelley
my word in your ear 
I love Shelley. Thanks for sharing this!