Females utterly defy logic and I am one. At the risk of catching a great deal of flack, when teenage girls push the envelope, and it occurs to them what's going to happen, it's a shock, they get scared and pull back. This is one major reason why young ladies should not have sex before marriage. They aren't emotionally prepared for it.
And guys, am I right, if a 16-year-old boy get that far along in the act, it darn near takes a club over the head to get him to stop? An ambiguous "I think I should go home now" isn't really blunt enough at that point, I'm thinking.
No flack from this former 16 y.o. boy. The reason is that you are correct on all points.