This did not happen to me, but to a friend of mine. He asked me to put it here, since he doesn't have his own account 
He met this girl, they had great chemistry, went on a couple of dates. He asks her to go steady, she says okay, but that people can't know about it. She doesn't make it completely clear why. Something about an ex-boyfriend. They then have sex, but during this she suddenly begins to cry. Won't tell him why. She stays for the night. The next morning she is her usual self, maybe a bit more quiet, he told me.
My first reaction to this was: "That bad at it, huh?" It was just a joke, but he got kind of upset. So obviously this means a lot to him.
Why did she cry?

He met this girl, they had great chemistry, went on a couple of dates. He asks her to go steady, she says okay, but that people can't know about it. She doesn't make it completely clear why. Something about an ex-boyfriend. They then have sex, but during this she suddenly begins to cry. Won't tell him why. She stays for the night. The next morning she is her usual self, maybe a bit more quiet, he told me.
My first reaction to this was: "That bad at it, huh?" It was just a joke, but he got kind of upset. So obviously this means a lot to him.
Why did she cry?