Slowly, I know every sitch is different, but your phrase about H thinking his A was a long-term deal, and his conviction clouding your own perspective too, hit me between the eyes. Even as I know that H and OW are having problems, I can barely believe it.
Four weeks for the houseguests? That's a long time. I hope you will have them doing dishes by the end since by then they will be part of the family!
Good luck with the dinner with the woman who may be having an affair, ick. Lost of steps to take, aren't there.