lol
you had it coming........now deal with it.
quite trying to hide behind the bushes and tell her straight up how you feel.
text/CALL her back and say "look, i feel like you putting too much on it. we fucked, we had a decent time......and now it's time to MOVE ON. I have no feelings towards you at all and i could NEVER see myself with someone like you. Don't take it personal"
or
"WE FLIRTED, WE MET, AND WE FUCKED. THAT'S IT, QUITE TRYING TO MAKE SOMETHING OUT OF NOTHING. YOU WERE A DECENT PIECE OF ASS AND YOU'RE FUCKING ANNOYING. STOP CALLING & TXTing LIKE A PSYCHO BITCH. I'M ON TO THE NEXT BITCH"
change your number and i hope it teaches you a lesson(most likely it won't).
unless you love the drama that comes with cheating i'd suggest you reevaluate your relationship with your MAIN and dump her too. that way you have the freedom of doing what you want without worring about your MAIN tripping about it.