A different perspective from a newcomer here. I think you are being disingenous here. I am not judging what you did, by the way, that is entirely up to you and the man you are/were involved with.
However, you went into this situation with your eyes open - you knew that he was in another relationship and you must have known that, at some level, this man was going to have to be deceitful towards his long term partner, at least for a period of time.
We don't know the full details (for instance does this man have children) but I presume that when you got involved, you must have been prepared for the relationship to be clandestine, at least for a bit, as in general no-one wants to be seen as a "home wrecker".
Unless he ever gave very clear indications that he was definitely going to exit his marriage for you, then you would have entered into some kind of agreement, even if unspoken, that neither of you were going to "spill the beans" without the other's consent.
Now that the proverbial sh** has hit the fan, the man is dithering and probably genuinely doesn't know what to do in the long run. Caught between a rock and a hard place, even if he only has himself to blame.
However, in my opinion, it is entirely up to him what he does in his marriage and what he tells his wife. Surely that is not up to you, after all you were prepared to enter into an illicit relationship in the first place? Now that things have turned sour you are playing poacher turned gamekeeper and toadying up to the wife.
Suppose the tables were turned and he decided to spill the beans about your clandestine relationship to his wife (or anyone else for that matter) without your knowledge or consent? How would you feel about all the dirty linen being aired to all and sundry.
Sorry, but I think you are being quite manipulative here. If I were in your situation I would have my head down and I would be getting on with my own life and letting the (ex) lover decide what he want to do in his primary relationship.
You are not a marriage guidance counsellor.
If I was his wife I would not demean myself by talking to you at all. Sorry to be blunt but I think you are pretending to befriend the wronged wife when you really have an ulterior motive - ie you are the spurned lover and by spilling all the beans to the wife you are adding insult to injury.
Sorry to be blunt but I think your motives have got nothing at all to do with caring about his wife.