I second one of the other commenters who says that the song is about the perception of being cheated on. It’s funny, after the first day I ever went on with my partner that song played and for a little while we considered it our song, then eventually kind of faded as they both realized the song didn’t relate to us very well. Now I can look back years later, after going through a lot of therapy and self enrichment and I can realize that those kind of paranoia really did plague our early relationship. I’m glad that we were able to move on from it