Savage Love Achievement
You gained the affection of SIE and allowed her to consummate her lust.
SIE is very different from the other romances in the game, as trying to be Professional or Suave with her will not work, as she prefers it when you play hard to get. That means all you have to do is choose mainly Aggressive answers with her. Romancing her also becomes much easier if you do Rome before Moscow, and choose her to help you out instead of Albatross in the mission "Intercept Surkov at US embassy" instead of Albatross. Make sure that you save her at the end of the mission "Assault Brayko's Mansion", or you will not be able to romance her.
Right before the final mission, you will be able to choose your handler. As before, choose SIE to help you out. She will eventually come to release you, but not before she gets what she wants. Stick with Aggressive answers as always, and when she comes onto you, allow her to have her way. Once done, the achievement will unlock.