Who said this???
the emperor! :]
(major spoilers for next arc)
this is pretty much his constant line of thinking after a series of traumatizing things happen:
-FL finds out/senses she will be leaving her current body
-she asks emperor to stay & spend this little bit of remaining time with her
-concubine suddenly asks for the emperor
-the emperor, torn between affection and a sense of duty/pity, chooses duty: he leaves empress to go to the concubine, promising he will be back immediately after seeing what the concubine needs (concubine just faked being sick)
-after he leaves, assassins appear, coinciding with the time the FL's soul leaves her current body
-emperor arrives to find kidnapped, and after chasing the kidnappers he arrives to her bleeding and holds her in his arms till she passed. he's stricken with guilt, further worsened by the fact that the FL had asked him to stay in (what he thinks is) her last moments.
-during this, the FL returns to her original body for two years
-in this time, the emperor becomes sort of unhinged and desolate after her death, both refusing to take any other empress to replace her and disallowing anyone to change/touch anything in the empress palace. his rule becomes tyrannical.
until more time passes and he sees a male guard visit the palace who reminds him so much of the empress. (weird translations on pronouns here so i couldn't tell if it was FL in disguise or her soul got transmigrated again to a different body when she decided to return to the emperor to protect him from an assassination attempt)
she end up being the emperor's body guard. the emperor begins to pursue him/her relentlessly and unlike before is very quick to confess he has unrequited feelings for her (in front of the whole court no less) and immediately begs/apologizes if he thinks he offended her.
the angst soon!!!
like, nah this is cute, sure! but this ain't enough to redeem you homie, i need the (spoiler) 'i put her aside & she died. so i chase after her shadows in everyone i see' part