The telling lyrics: "The ties were black, the lies were white / The shades of gray in candlelight / I wanted to leave him / I needed a reason"
Who it's supposed to be about: Tom Hiddleston
Why? The black-tie event Swift mentions references the 2016 Met Gala where Swift and Hiddleston first met, though she was still dating Calvin Harris at the time. It seems like she could be alluding to the fact that she started dating Hiddleston as a reason to leave Harris.