I can tell you that the A is going to die, although it might take time. STBXH told me that he hadn't introduced OW to the kids because in a couple of years there could be someone else.

As one of my friend pointed out, him saying that about his lover for 3 year says a lot about what he thinks about her. Not a relationship in the ling term for him, so not worth it to introduce her to kids. Still can't believe that he has destroyed his family life for someone who he doesn't see a future with! Will he wake up? I think he is perfectly aware of what he does and used OW has an escape because he couldn't face to walk our on his second set of children like he did the first time!
COWARD is the word that crosses my mind, on the other hand I know he won't come back and now I'm getting fine with it.

You are still new in your story and it will take time and eventually you will feel indifference for WAS allowing you to move on!