Of the posts you mention (I've seen them too), what strikes me is not the fact they had sex, but the fact that they can't have a basic conversation. You can open your legs for a guy but you can't discuss a what type of relationship it is? WTF is wrong with these women?
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Why does it have to be one or the other? My partner and I managed to shag each other to bits in between discussing those things you mentioned above and generally getting to know each other. Had we been incompatible, we would have gone our separate ways with some rather terrific dirty memories. But we were compatible and the fact that we had first day sex didn't change that.