We dated for two years, then she came to me and admitted that she'd never loved me and only agreed to date me in the first place because she wanted to see what having a boyfriend was like and kept the lie up because she liked the sex and affection I gave her, and also that she'd been cheating on for the last four months.
After breaking up with her, I kept finding out more and more lies she'd told me to try and turn me against her friends, like characterising one as a creep who wouldn't take no for an answer and kept trying to convince her to dump me for him even to the point of cutting himself on camera as emotional manipulation. None of that happened, she just thought it would be funny to see me not like him.
She would also share all the intimately private information about me that I told her with her friends, fully knowing that they were things I didn't share with people normally and felt self-conscious about.
And finally, during the time when I was still in denial and still loved her, she would keep telling me how she still cared about my feelings and wanted to be with me and told me that she wasn't with anyone else so I'd stay wound around her finger, when really she'd hooked up with another guy the same day I broke up with her and had no interest in me anymore.