Great! A story about the end of the world. Now that December 21, 2012 is a week into the past, the story almost feels dated, but I guess that happens sometimes. I enjoyed reading this and I found the narrator to be an intriguing person in the sense that she wants to save herself for marriage, but is also very sexual. (By the way, this is getting a bit picky, but you confuse the words, celibacy and chastity. The latter is not having sex, while the former is not being married. Even George Carlin made jokes about this.) Mike sounds like an interesting character, although I felt like I didn't know him well enough.

While we're on the subject of vocabulary, you use several sexual slang words which, I admit, I don't completely understand. Another technical criticism is that you use the word "laid", when I think you mean "lay."

Actually, maybe this would work better as part of a longer work. We could get a better idea of Mike's relationship with the narrator, and how it developed, but also it might be interesting to hear about what their relationship is like afterwards presuming that the world didn't end. What does it mean for two people who decided to have sex, because they thought the world would end, when things go right on as normal? I imagine it would be kind of thorny.