So, from everything I've read so far, this smells like an exit affair. Not much hope here - there is little chance that he will want to reconcile and return to the marriage. His new relationship isn't likely to last either, but what's that to me?
Anyone have any advice/information regarding exit affairs?
From what I have read, and some of the success stories I have heard since I started doing my research after BD, there is always hope! I have heard some incredible stories of things including a spouse marrying someone new, only to return a couple of years later to tell the LBS that it was a mistake and that they want to come back. So even as dire as your situation feels, there is always hope he will realize what he is doing and want to correct it.
As far as exit affairs, I am not sure that changes anything from DBing standpoint? The overall principles still apply: detach, work on you, GAL, be the best you can be and show that you to him every chance you get.
M(53), W(54),D(19) M-23, T-25 Bomb Drop - Dec.23, 2017 Ring and Piecing since March 2018