Do you believe in karma?

my ex is getting her karma for all the things she has done to me and others. she played me to get over her ex, she kept me on the hook while she got together with someone else (who was in a relationship which she broke up). recently she even kissed me and hugged me despite saying she had no feelings for me. i was more or less her yoyo. and i believe in karma, because now her bf dumped her for her friend. she's miserable. what i don't understand was why it happened to me. was it my karma? or was i just a victim of someone elses cruelty?