First off, why in the blue hell do you care if this B#T$H has a boyfriend or not?
Do you need closure?
Can you not go out into the world and get yourself another g/f?
Let me generalize, most women like attention; it's what they crave. You, my friend, must feel that she's the only one ( your one and only soulmate). If you want to know the truth, she doesn't owe you anything. It's her life!
Get this through your head, you don't owe her anythng, either. If you can, avoid this B#T$H.
Here is your first lesson, "Never date a co-worker if you value your job". If there is a possibility, ask for a transfer to another location. You will feel so much better.
Second, why should you care if this fool is running her "motor" mouth about you hooking up with another female. You should say that you are a stud. If you are a "nice" guy and it bothers you to say that you are a stud or something cocky, just say "whatever" or "if you say so" and just ignore her.
Here's something to comtemplate. The more you deny these rumors about yourself, the more this B#T$H knows that she's hurting you by "rubbing it in" and that you will be a P#SSY in accepting her back in a relationship if it doesn't work out with her Joe Shmol Sancho.
HERE'S A NEWSFLASH: YOU'RE 18!!!!!
It's not the end of the world. You have your life ahead of yourself. Don't get into a relationship. Have you ever heard of "hooking up"?
Lesson #2: Don't be P#SSY wiped! You are nobody's doormat unless if that's what you like, which I hope not.
And the Third Point, eliminate any form of communication with this B#T$H. If you have her phone #, delete it and if she calls, don't pick it up, she will get the message. If you have her on Myspace, Facebook, Twitter, or other internet social network, delete her and avoid any messages, instant messages, and looks to her profile. What if she e-mails you, delete it. You have to move on with your life.
"What if it's easier said than done because I'm 18 and she's 17 and nobody knows how much I love her and because she is the only one and I won't find someone like her?" Just find a hobby.
Listen to your friends. Go out, have fun, enjoy life. The more fun that you have, the quicker you can put this rancid memory in the back of your head.
In conclusion, you should go to college. OMG! You cannot believe how many women you will find. Whether it's community college or a four year institution, your supply is endless, if that's what you want, which happens to be a secret desire of all guys (heterosexual, that is).
--------Get an education, join a study group, enter a school club, and graduate to get yourself a better job. Just feel good about yourself that you DUMP THAT B#T$H.
Good luck with your life, amigo.
P.S. If you are about to have sex, ALWAYS wear a condom. Don't let one night a pleasure ruin 216 months of your life (18 years of child support). Never believe that a woman is on the "pill".