GM, I'm sorry you're going through this. But in your posts, a few things stood out.
1) The four way meeting. Bea gave some great suggestions. Go into it knowing what you will and won't settle for. Get an agenda. Don't go in unprepared and having to make choices you haven't thought about. 2) If you're still, you'll know all the hidden things you didn't know before. You may not want to but I have yet to see a case where that which is hidden didn't come to the light at some point. 3) Your H is off the rails 4) Your H has been hiding things for so long, it must be tiring, right? That said, he'll tell you things because he simply can't keep another secret. It'll seem odd to you, the things he tells you. 5) You're right to be suspicious. He's off the rails. 6) You should check with your attorney about exposing your H's affair with his subordinate. If you expose him, you'll get immediate satisfaction. He'll get fired. You'll lose the alimony, payments, etc. Your kids won't be able to benefit from his finances either and it'll be because of your actions to expose it. That's a possibility, but check with your A. It may be that there are no repercussions. If it helps, I had to make a similar choice about suing the OM. I can do that in this state for alienation of affection. I chose not to because it would drag things on and expose the kids mother. There was no other benefit to me except money and revenge. And I'm not interested in either of those.
Time to reset your expectations. They should be at zero when it comes to him. He can't live up to anything else right now. He may never, but for now he will not.
As far as what he thinks of you as a mother? Let's look at that again. He's having an affair with a subordinate, hiding it, lying, gambling, and treating you like dirt. Are you really worried about what he thinks? Should you be? I wouldn't. In my own situation I don't and I do know how difficult that is to no longer trust somebody you trusted for a long time. But it's the reality of the situation.
Some things to think about.
Peace, AJ
"Our lives begin to end the day we become silent about things that matter" MLK Put the glass down... "Yesterday I was clever so I wanted to change the world Today I am wise, so I am changing myself."