Why don't you happily suggest to H that you both go, and if PW shows up you can bail and do XYZ instead. Make the XYZ something fun and sexy...
"H, we can't control whether PW goes to the party or not, all we can do is control our actions. So, lets plan to go to the party and have a good time. If she shows up, we can bail, I promise to show you a good time anyway..."
