PVRIS has stated this song is themed around ghosts, which they tend to base quite some of their music and videos on. This is to be found in the "You're a cold air" and "I caught you walking straight through my walls"
Though, to me it also feels like it is written about an abusive relationship. The part in which the narrator notices the influence of the significant other and is finding the courage to leave them. This is a very powerful moment in someone's life and hard to reach, since they're used to being scared. Verse 2, and especially the part "Under sheets avoiding you" shows this fear. That she is still singing about that shows that somewhere, this feeling of fear is still present, but the powerful realisation dominates this feeling. This all is perfectly in line with the power present in the music and song itself.