I completely agree with you. He is not yet a fiancé, she is not even divorced neither is the affair partner. Very bad taste to introduce this man into the family at this stage. If she said she stopped seeing him earlier, I am guessing deep inside she knew what she was loosing. This affair partner will not last long enough to spend next Thanksgiving with you. Reality has kicked in trust me. The romance she thought so perfect is starting to fade. She will have to deal with kids of 2 previous relationships. I would not get to involved simply cause it is not going to last. Make sure she understand you do not approve her bringing the affair partner unannounced, cause she is STILL married.