For the following reasons, I wouldn't want to have sex with someone who isn't my wife, also wouldn't wanna risk getting a girl pregnant, and last of all, sex... any kind of sexual activity outside of marriage is considered a sin in most Religions. I'm a Christian by the way.
Yes, I'll freely admit, I make up beautifully-crafted lies if other guys ask if I had sex before. I'll tell them a couple lies, so I don't look like a loser. I haven't had sex yet, I'm strongly considering waiting till Marriage.