itch.io

Basically accepting sexual favours for money enough times will grant you the perk

You have to accept a sexual favour for money once then it becomes easier your character to accept more sexual favours

Working in the bar is the easiest way to do this cuz you will be bombarded with requests for sexual acts

Another way is to do the Haven mission. There you meet and befriend Kitty. After the mission you can meet Kitty in the Truck stop area and after some convincing, she will show you the ropes.