So let’s say a guy and a girl have been dating for a few years, and things are going well - there are no real issues in the relationship. The guy’s coming home from a bar one night, kind of drunk, and he runs into a female neighbor that he’s seen in the hallway a few times - they’re on friendly terms, but they don’t really know each other or anything. She’s also drunk. They strike up a conversation and decide to go to her apartment to have one more drink.
So because they’re drunk, their conversation is loose and turns flirtatious. At some point she lets slip that she has a weird sexual quirk - she can only have an orgasm if a man watches her masturbate. So things heat up and - though they never touch at all or kiss or anything - the guy ends up watching the girl get herself off. And then he goes home, end of story.
He tells his girlfriend and she breaks up with him. He thinks she’s completely overreacting.