So, because I've seen a post get boosted that gets this very wrong, I'd like to just offer some clarity, as somebody who is asexual...

Asexuality is not the choice to not have sex. That's celibacy. Asexuality is not having sexual attraction to another person. That attraction that causes people to have the desire to have sex is what is absent for asexual people.

Asexual people can and might have sex, if they want to. That's not what makes them asexual, and having sex doesn't mean you're not asexual.

Here's AVEN's explanation too, for anybody who wants to know more!
http://asexuality.org/?q=overview.html