Pour a little salt we were never here
Salt has healing properties, when put on open wound they help the process along. Probably metaphorically speaking, he wants this doomed relationship to heal, to even Just last the year.
He then basically tells her to let him go, to cut off the tethers binding him to her
One of the more opaque metaphors, it could be a reference to pouring salt on wounds (making an open wound more painful), taking with a grain of salt (recognizing that something may be exaggerated), even possibly the practice of throwing salt over your shoulder for luck or the superstition that spilling salt is bad luck.
However, the second half of the line we were never here seems to indicate that this is likely a reference to salting the earth (not to be mistaken with salt of the earth), an old practice of cursing destroyed cities by sprinkling salt on the ground. Using this interpretation, the line refers to the Vernon’s wish to eradicate his old relationship, never to return to or rekindle it.
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