Was she trying to get back at me?

I started flirting with my girlfriend's friend at work, somehow my girlfriend found out and dumped me and then when I asked out her friend her friend said no, I am hurt because how can my girlfriend sabotage my plan to go out with this girl, she is a jerk, and now I feel played. She also posed herself on fb under a different name, was she trying to see how vulnerable I really was? How can she mess around like that?