Since Mindflayers dont have feelings, I believe any Romance with the Emperor should just have the character dying.
(He even sais in the game the emperor is using Humans only as thralls and tools. )
There is an in-game reason given for why that should not be the case. Essentially
the Emperor was not happy with how his last thrall turned out. Consequently, he attempts to honey trap the player. He will not harm you unless it benefits him. Although, by his account, he is unable to feel "anything", he is willing to just let you go once freed. Pro-social psychopath vibes much?
Also, @ op, he kind of has a post ending talk with the player if you are
