No, they never had sex, right? It was just the pretty guy's fantasy.
At first it seems like a fantasy after the flashbacks rolled and ended with them back at the cafe, Hermi looking at the brother drunk and asleep, but after that the chapter goes back to them doing it at the end and Hermi confessing. The easiest way to have implied the falling action after the climax (in the story line) in such a short story is to have had them actually been doing it at the time that it showed them doing it and them having confessed. Otherwise, the story would have been unfinished. Clearly the sister wouldn't have had a chance anyway since the guy loved the brother, and the last several pages (flashbacks) were all implied falling action as they did it and the top confessed. Also, when they did it, it was too real in the story to have been his "fantasy" I would have to say.
Was the sister just abandoned drunk in the bar? ...