A situation…

Seeing that I was friends with someone for a year straight, had some flirtatious and other types of moments, and them almost purposely attempting to lead me on (to little avail since I did not particularly want or care for any relationship with them) just to find out that for a year straight they had been on “break” with someone and NOW after they had invested so much time, and so much energy into this friendship that they had turned into their own internal situationship suddenly tells me that I have been practically the one they had been using to cheat on the other? 

Not only am I baffled by this situation I am disgusted with myself for being put in such a situation, and the audacity for them to ask me to meet them at some point like nothing ever happened is tragic and terrible. I feel ashamed, and I cannot imagine what it actually would take for such a decision to be made.