It is so hard to be in the middle! One of my brothers is an alcoholic and when he was having problems decided my parents were angry at him so both he and my parents used me to find out about the other, like I knew! As you point out, we have enough trouble with ourselves and don't need other people's, especially our parents (and older siblings :-) problems!

I would tell your parents to talk to each other, not you. If she arrived at the hotel/was checking in and didn't want to see you I would have said, "bye" and not let her call me later and not have told my father anything other than "call her the %#@&#! yourself!" :-)

I wouldn't speculate who she is in the bar with (or where she is) and why; if your father wants to do that, fine, but if you can't be there and see/know for sure, you can drive yourself crazier with your imagination making stuff up.