Bit of a long story but I hope I can keep it short.
DH has a good friend who he has known since school. Let's call him A. A also went to university with myself and DH, lived on our sofa at one point (student house), organised DH's stag do - has always been about. A couple of years out of uni he met his lovely wife B, and had two DCs with them who we've got to know pretty well also. We've babysat for each other, had family days out, been round each other's houses and generally been good friends.
Various upsetting things happened to A and B (which I won't go into for reasons of identification) and their marriage started to suffer. It finally came to a head about three months ago when A left B for another woman who it turned out he'd been having an affair with for some time. Since he left it's all become pretty bitter with both A and B using the children as weapons against each other (e.g. - A introduced the OW to the children without telling B so she wouldn't let them go to see him next time he was due to have them because she said she didn't trust him, so he decided to not give her some money she was counting on - they both calmed down after a while and compromised but it was hell).
DH and I have tried to stay out of it and not take sides but it's becoming increasingly difficult. Now A wants us to come to a dinner party hosted by him and the OW. DH thinks we should go because A is our old friend and he isn't willing to drop him. I know B will feel really betrayed and hurt by our socialing with the OW and A when everything is so up in the air and think it's too soon and we should try and avoid OW. I keep thinking how devastated I would be in B's shoes.
DH and I have been arguing about this all day. Advice? AIBU?