re: Had this girl I'm dating drop the E bomb (exclusive) on me

Jesus....what a bunch of delusional white knights we have here. How old are y'all? If you're 50+, then I can understand your lack of experience with 95% of modern young women. Otherwise...yikes. I don't envy your rude awakenings.

OP:
They feel the need to say this because it's what they're feeling at the moment, like anything else.

Similarly, she'll be "exclusive" right up until the moment she feels like not being exclusive, and/or her rationalization hamster can invent a flimsy reason to explain away any desired lapse. If after said lapse she changes her mind and remembers why she originally wanted to be exclusive, she'll just invent a reason in her mind that it didn't count (she was drunk, it was just once, just the tip, she was mad, etc) and if she's not an idiot you'll never even know. I've *been* that temporary reason enough times (usually unwittingly, until hearing them tell me about it afterward) to know the ugly truth of this.

So...you made the right call. That 5% (if that) of gals worth keeping around and mayyybe being exclusive with tend to be easily identifiable and have the self-worth to not need to demand exclusivity...just as people who are respectable don't "demand" respect. If she presented you with her desire to be your girlfriend and didn't immediately politely reject your answer and move on (since unicorns know their worth), then she's not one of that 5% and you owe her nothing. Sounds like a mild manipulation attempt...nothing more. Par for the course. Carry on.