The song, which is one of the vault tracks from her latest album Midnights, is seemingly about a dying relationship where the narrator begs their partner to “do something” or “say something” to save the relationship. Many fans believe this song is about Taylor and her ex Joe Alwyn, who publicly broke up earlier this year.
Source: https://www.buzzfeed.com/laurengarafano/taylor-swift-jack-antonoff-youre-losing-me-reactions