Heavy Act 3 spoilers incoming
*** Spoiler - click to reveal *** The objective is straightforward, choose dialogue choices that will allow you to romance the emperor after you discover his true identity at the end of act 2/ beginning of act 3. Assuming you didn't allow Gale to blow himself up and end the game in act 2, you will soon discover the true identity of your dream visitor at the end of this act. After finding out that the dream visitor is actually an illithid that goes by the name of "the emperor" you will have various dialogue options in how you can interact with him. In order to unlock this achievement, choose generally positive and accepting dialogue towards him and definitely do not try to kill him. After the initial cutscene where you meet the emperor ends, continue along through Rivington and Wyrm's crossing in Act 3. After a few long rests, you will have the opportunity to speak to the emperor in the astral prism and learn more about him. Again choose positive/accepting dialogue here, you will even have a chance to hold his hand in comfort. A few long rests after this and you will again meet him in the astral prism, where he is shirtless and this is where you will have the opportunity to have sex with him. Again choose positive/flirty dialogue and you will have the option of having sex with him (note you can choose to do this with his illithid body or have him revert to the dream visitor form, you will get the achievement regardless of which you choose) and that's all there is to it!