This achievement is story related and is (normally) unmissable.
The last quest is called Wedding Horns. The achievement should pop when you complete that quest, and before returning to Randvi.
If it didn't pop as soon as the screen show that the story arc is completed, you have to reload a save, and redo the end. I had an autosave just 2 minutes before the end.
You may need to reload the entire game as well, as quick resume seems to mess with the game. Once I did that it popped immediately. Hopefully for you all as well.