In some sense finding out about this has made me feel a lot better.
I suppose i see a lot of what XH has been doing with OW as driven by the money she provides him (rather than a 'real' relationship).
On the other hand, it has pretty much quelled any hope I have of him ever being able to extract himself from his current way of living/thinking.
There comes a point when things are so hopeless financially that there is no possibility of getting out.
Anyway, this knowledge of what's been going on is starting to give me a much needed sense of closure.
I think it's been the flabbergasting nature of what's happened to my M that has thrown me for so long. There was just no explanation for why or how the specifics were unfolding the way they were.
Now I am starting to see what was going on, and it all begins to make sense.