If you're top, dominant and have high enough reputation among bandits and werewolves you should be able to fuck them
The good news is that you don't need a good reputation (even if they hate you you can still fuck them), you don't need to be a top or dominant, you don't need your skills higher than 10, your battle experience more than beginner and your sexual experience more than skilled. The bad news is that I don't know what you need, sorry! I'll write down if I can find what triggers it.
Edit: Are you playing as a male or female?