I'm sorry to hear about the rumors of your past coming up. Unfortunately, because the ruthlessness of high school gossip typically puts Hollywood tabloid magazines to shame, there's no guarantee that it will end before you graduate. While that may not be consoling to hear, your example of purity to those who know you will speak louder than some girl's gossip. If a guy really loves you, then he will be able to see beyond your past--even if it is true--to see who you are today. It was probably out of jealousy that your "friend" said that about you. Sometimes girls are so insecure that they are willing to sacrifice a friendship for the passing security of having a boy by their side.
In regards to your future, you will only end up with a jerk if you choose to settle for a jerk. Plain and simple, girls get what they settle for. Sometimes it's hard to see beyond the four walls of your school, but don't let the rumors hold you down. You're bigger than them. As a comfort to you, realize that I graduated from a school of more than 1,000 students, and as of today, I am in touch with only one of them.
Unfortunately, you still have to deal with your classmates as long as they're you're classmates. The more immature a group is, the more likely you'll have to put up with gossip. But in one way or another, you'll live with gossip until the day you die. If we spend all of our energy trying to stop it, then we'll wear ourselves out pretty quickly. Instead of letting the rumors rob us of our peace, pray for whoever is spreading them, and forgive her. You've got to be pretty sad inside to have to try to ruin other people's lives in order for yours to go better. So, in a sense, you should feel sorry for whoever is spreading the rumors.
It's bad enough for rumors to float around, but it's certainly worse when your "friends" are contributing to it. You may have heard the expression "with friends like that, who needs enemies?" If your friends are stabbing you in the back, step number one is to find better friends. After all, you're the only one who chooses them. When you select friends in the future, remember this unchanging truth: "Those who gossip to you will gossip about you."
Also, make sure you don't gossip. Be classy. Never say anything about another person that you would never say in front of them. The Scriptures tell us that we will render an account for every single word we speak, and that everything whispered in private will be declared to all. So, make sure that you're not commiting the same fault of gossiping. When all is said and done, the girl who gossips about you will end up with the worse reputation, for gossiping and betraying a friend.