She talked crap about him the whole time we hung out, and has told me repeatedly that she is going to dump him for our love.
Yea.. they alllllllllll say that. It's your own fault you're feeling the way you are for getting with a woman you knew was in a relationship. Next time a woman tries to play you by telling you how shitty her relationship is, tell her to leave him then and then YOU get the hell away from her. Don't be a fool twice, learn from this. Never talk to her again, forgive yourself for being naive and falling for her lies and go zero contact with her "nasty ass."
“The willingness to accept responsibility for one’s own life is the source from which self-respect springs.” ~Joan Didion