It's unclear if the writer made "Margot" a version of her younger self, or if it as a completely fictitious invention.
I could believe it either way.
She probably did at least have an experience of her own where she wanted to reject a man during the "late stage" of a date shortly before sex would normally happen, and felt uncomfortable doing so.
She didn't seem to understand men very well. The Robert character was all over the place, and that ending was totally out of character. It was like she lifted it from dating site tales where some guys get inexplicably rude and obscene after getting turned down. Totally didn't fit with the rest of the story. Remember, one part of the story had Margot's roommate sending a blunt rejection via text to Robert (as Margot), and he responded very politely. Then, later, after seeing her at a bar with another guy and avoiding him, he still texted her politely. The ending was lazy writing, plain and simple. Plus the author just doesn't understand men.
This is actually a common problem in fiction writing. Women sometimes have a hard time writing for male characters, and vice versa.