Where do we go from here? FWB, BF-GF, or nothing?

She's obviously not ready to give up on her boyfriend and you'd be setting yourself up for disappointment if you pursued her. She is not available to you emotionally and until she makes the decision to step away from this guy she never will be. You can continue to talk to her as friends, but don't bring up your feelings for her. In fact, try to appear as though you are no longer interested in anything but friendship with her. Be aloof and unaccomodating. People want what they think they can't have.