What I suggest you do is to stop having sex with her completely right now, I know this will be difficult; but see if you guys can spend time together enjoying each others company without the sex. You will see how much you have in common, if you can truly communicate, and if she is intriguing to you -beyond the sex. Set a time limit like 6 weeks to see how you guys do. If you have great sex now, you will still have great sex in 6 weeks, but it is worth the experiment to find out if she is someone you can commit the rest of your life to. Take it from me, after being married for awhile the sex won't be as heated as it is now, but the true reward comes from actually liking your partner and having something to talk about. They always say that you have to have something to fall back on when the spark turns to a soft glow...this is true! I can tell that you have very strong feelings -this could be why the sex is so good, but you can't let the sex muddle your brain when you are considering a commitment as large as marriage!
Good luck to you!!