There are a ton of reasons you could have sex, for example:
One night stand.
Or you just feel like it.
There are also a ton of reasons you don't want to have sex, for example:
Low sex drive.
Or you just don't feel like it.
Regardless of whatever reason you choose to have sex, or not have sex, it's not that big of a deal.
I say that sex isn't that big of a deal because having sex, or not having sex, is nothing to be ashamed about.
Having sex doesn't make you a whore, and not having sex doesn't make you a prude.
Have sex, or don't have sex, because that's what you want to do– it's your choice.
Be honest and open, and you'll know that the right people will respect you for the choice(s) you make.