In Undertow Lyrics
I think the speaker's significant other made a huge mistake which she cannot forgive. The speaker doesn't want to rely on hope and faith anymore (won't rely on the moon for anything)
The SO should let go, because there's no turning back after a huge mistake that should've never happened in the first place. An unforgivable mistake.
What I like about this song is that it's written as if it's from the singer's perspective, and that her partner has wronged her, but it's not exactly just her perspective because she's putting herself in his shoes and being understanding. She doesn't fully forgive, "Meditate, play solitaire, take up self-defense, When you get old and faded out will you want your friends?" She's in a depression, she's in a post-breakup identity crisis, but they, the pair of them, "toss and turn in undertow."