<human>: Can you succinctly summarize the text in 1-3 sentences?

So, I recently met, and messaged a woman on an online dating site. Held a conversation with her, getting to know her a bit, standard practices when looking for a relationship. About half way through, after mention some of my family members and their professions. She begins asking me particularly a lot about my brother in law. And eventually asks for my sister's name. And as you expect, she knows them. Now, the conversation should have ended here. But, the idea of simply pretending we did not figure this little hiccup out crossed our minds. And the conversation grew very sexual as we both became turned on by the thought of this little taboo. Suffice to say, two days of non-stop texting, and we met. No date, no games, straight to sex. Now, the fuck up is. Though it was most certainly an exciting evening, that was solely furthered by the taboo not her personality or appearance, not to say she is an unattractive woman, but she is not my typical type. The sex in hind site was, okay at best, and personally I would rather not continue the 'affair' any longer that one time. However, I am now stuck in a dilemma, how do I approach this woman to call off this situation. I know I will be judged by my typical move, which is if a date does not go well in my mind or I am not attracted once meeting, I simply drop contact. But the fact that this woman knows my family and apparently had a fling with my brother in law at some point in the distant past, which she mentioned after coitus, makes this a little challenging. As I do not want to be blackmailed into anything. I get the vibe she would not tell the family. But if I present this cancellation poorly I feel like she might force my hand. So now I'm stuck here trying to figure out a good excuse.
<bot>: A horny man had sex with a friend of his sister and her husbands. He wants to leave as a one-time thing, but he is worried about being blackmailed.