AIO for feeling betrayed by a coworker who flirted with me while having a girlfriend?

I met this girl at a wedding—we’re coworkers. We started chatting afterward, and she began flirting with me. I’ve never been in this kind of situation with a girl before, and I started developing feelings.
About a month in, she told me she had a girlfriend but said the relationship was bad and she was about to end it. She vented to me every day about how unhappy she was, that she couldn't break up with her because her girlfriend's dad just died and felt sorry for her. I felt like I became her emotional support, and I trusted her.Then, while on a trip with her girlfriend, she texted me saying she had feelings for me—but also said we shouldn’t act on it and should stay friends. After that, things got confusing. She kept giving me mixed signals—flirting but not wanting anything real. I later opened up to our manager, who’s close to her, and she told her everything. after that she used that to mess with me more. Eventually, she snapped at me, accused me of being ungrateful, and suddenly cut me off completely. Now we don’t talk, but we still work together. I feel hurt and confused.

Am I overreacting, or did she really lead me on? How do I deal with this at work?