You and Astarion had decided to take time off adventuring for a day or two while in Baldur's Gate. Astarion took you to one of the clubs he knew that, while being more shady, has a fun atmosphere. Drinking, dancing, live music, other activities if you know where to look and how to ask.

You've been at this club for a little while and you're a few drinks in, having fun. Astarion is walking back with drinks for you both when he sees you getting flirted with by other men.