Another involved process, but not necessarily hard. After finishing Saudi Arabia, you will meet Scarlet Lake. Scarlet isn't a fan of men who only try to woo her, so the usual Professional responses work well here. She's doesn't mind flirting from time to time, so it's okay to be Suave every so often, just be sure that you don't try to mix it in with business. Whenever it comes to the mission at hand, be professional with her. Also, if you constantly explore each level, every so often you will find an email that will be damaging to Halbech's reputation. Whenever you get one, make sure to send it over to Scarlet right away. The money isn't as good as sending it to your other options, but you'll earn like points with her very quickly.
Right before the final mission in the game, you will finally have the chance to meet up with Scarlet one more time. For this part, she will finally start asking what you've been up to the whole game. At this point, just choose nothing but Honest answers. Towards the end of this conversation, she will ask if you would like to spend the night. Say yes, and the achievement is yours.