Lyric discussion by patrickscheper 

Cover art for In Undertow lyrics by Alvvays

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.

My Opinion