As with everything else, it is an individual thing... I honestly believe that you should live with someone before you get married, how do you not know that you aren't going to drive eachother insane? I come from a fairly strict Catholic upbringing, and my parents lived together before marriage, and so did my older sister, and my older brother, live with their fiances before they got married.
as for the sex, I can only speak from personal experience. I was not an ugly person, nor was I the best looking... I think a little better than average.... I had chances for sex, many, but I never did. I finally met the woman I believed I was going to marry (in fact, I was actually engaged to her). She is still the only woman I have ever had sex with. But... as Curling said about STD's... I found out she was cheating on me because they found out at my Army physical that I had Chlymidia. (sp?) So... basically, I took all the precautions I thought were necessary, only had sex with the woman I thought I would marry, and still wound up with an STD. I can't really say I regret waiting now, and not nailing everything I could, but in a way, I wish I would have taken more chances and enjoyed more than I did...