Lyric discussion by ashwalk 

This is a longshot, but here goes:

-a deceiving, killer who tricks another killer to commit suicide with him, but stays alive.

Man muses the notion of having the company of this woman, suggesting they'll enjoy each other, because they're similar. The woman has killed her family and is in a state of mixed confusion and regret. He is a seasoned killer himself, and he actually thinks that her dying would bring her peace, so he uses this discourse to convince her of drowning.

She probably drowned her family. He will either drown her or leave her in a shallow pool "resting in a stream" after killed. He observes that she is decaying in life (metaphorically drowning), and implies that he is as well (possibly as a blind persuasion). So he suggests that they just go ahead and finally drown (this time literally - meaning he'll die with her), but actually he never intended to die - as seen by the marks his car left in a hurry where he dumped her body.

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