Well she says she was 'moved' to do it. However, she knew what she had told me prior, as in, they were not even dating at the time. I read this informative link I found in the general discussion forum about cheating in a poly relationship. It talked about getting "caught up" in the moment, but how humans have the power to control their actions. It also talks about owning ones actions, in this case, she hasn't done that.
She withheld the information to protect her own feelings. If she wanted to protect mine, and cared about how I felt, she would have been honest from the start and she wouldn't have gone down on the guy. That's how I feel. I don't think my feelings were considered in this, and that seems to be the problem along with feeling lied to... I'm not sure where it is going to go from here. We're going to counseling tomorrow, hopefully we can actually cover some ground.