girl, you will get through apathy and then you may get...mad. Verrry mad. And your H will be there to face all that. How he handles it will be interesting and telling.
If H and OW continue to work together, it wont work. Because you will drive yourself crazy about their encounters and they may go back to reconnecting. So, that is something to think about IMO.
6 years is a long time. He obviously feels it as "normal". You and her are different parts of his life (although it sounds he had managed to have you both mixed and that's weird). I dont think you will ever be able to explain.
I would kick him out. Just to get my act together. Just to see that this is SERIOUS. Sounds like he is downplaying it a bit, no?
My mom had a huge acoustic nevrinoma. We had the surgery in Germany, in a micro neuro center we were advised was the best. She had no side effects. NONE. We were doubting she had that 10 hour operation. She had lost the 50% of her hearing on one ear before the operation and that didnt change. I am sorry for your friend.
