JWS, I keep telling myself that it doesn't matter if W is faithful or not, I love her and I'm working on me and on this M. Then, I don't let my thoughts go down that path.
One thing I'm dealing with right now which I think is talked about in DR is that I'm starting to see some changes that could be positive changes. That tiny little bit of hope has also opened to door to the angry room and a little bit has escaped. I suspect this is very common for the LBS to push the anger aside while DBing and fighting to save things and then when the efforts start to bear fruit, the anger at their hurt comes rushing back to the forefront.
I mention that because whether my W is faithful or not, her behavior has been unacceptable and hurtful to me and some how there has to be a reckoning with my feelings. That reckoning may never include her, I don't know, but, it's something of which you should be aware.