Problem with a manipulative hb need some advice on this

Hey guys well in my class i started to have sex with this hb that atfirst was going super well i was thinking i had the control but then a new guy came in the class and she was with both at the sametime.But it messed up my mind coz i fell for her and i was thinking she was having sex with the other dude and the dude was really anoying it got to the point that he was ackting like me in every way and we nearly got in a fight.Well she said she wanted to just be friends with both of us and i said no and said you knew what you were geting into. Well since then the things arent the same the dude left the school and im okey with the girl BUT i found out then that shes the type of manipulative hb that if u havent ever been with one you dont realize since they do it so good.Even thou she said she wanted to be friends i said i got to think about it and 2 weeks without talking to her we ended up kissclosing after a party that i got pissed and dident give a f...k and a 2nd time with out beeing pissed.My Question is how can i use her weapons against her ? if thats possible I really need help on this so i dont have the same prob with anotherone.