Please don't take some of the above posts seriously and practice with a callgirl. That is one of the most ridiculous things I've read in this forum and some things I've read have been pretty ridiculous. Like a condom is going to prevent disease and his partner will be much more attracted to him knowing he's been practicing with someone he paid for. Yuck!
I would hope you have chosen someone who is not just interested in the sex part of your relationship. Trust me...I LOVE sex but the rest of the relationship is just as if not more important...and the most potent sex organ you can learn to turn on is her brain. Understand that you aren't going to be "Mr. Wonderlover" in 2 sessions and RELAX! If she loves and cares about you then she will unserstand and do her part to help you along. If not then she doesn't deserve your virginity.
Before my hubby and I married we were living in different countries and didn't have sex before we were married. We did talk about it a bit so I had some idea of what to expect but I was able to determine he was the one for me by how we related to each other...not by the sex part...which, by the way, we turned out to be perfectly suited for each other.
Sex itself can be a constantly evolving activity and usually is if one or the other makes the effort. So please don't rush yourself...you've gone this long...it would be a shame for you to give it up to the wrong person only to be rejected later...or for you to be so anxious about this aspect of your relationship that you forget to enjoy the rest.