Well, TnD, we all know who the delusional person is in your R, but there is nothing you can do about what he says and does. You can't control the situation, and especially not him. You can only control yourself and your responses. So, firstly get it into your head that you are NOT to blame for this crisis. Nothing you did or didn't do would've changed anything. He's blaming you so that he won't feel guilty ... so that he can justify his choices/actions.
You may have heard all this before, but it bears repeating (and as a reminder to myself, truth be told):
How to move forward from here? Don't discuss your R ... it just ends up in an argument ... not good for the kids to see (if they saw or heard anything). Do protect yourself financially, seek legal advice about your rights and protection during a S or D, just in case ... don't have to start the proceedings, but it would be a good idea to know what you're heading into if it goes that way.
Detach, detach, detach is the mantra on this board. It's hard to do, but once done you will find peace, and the children will feel safer. At this moment, they are feeling the tension. If your H wants to talk about the R, just listen. If he blames you for whatever, just listen, don't defend the indefensible. Deep down he knows he's being ridiculous, but when you try and defend yourself, he's got a justifiable argument. It's what he wants.
You must work on you, to be a person in your own right, separate from him. We shouldn't need our spouses (emotionally speaking), but want is another thing. It's take me more than 7 years to get that. Right now I don't need or want my H. The "want" could change, but I will never allow myself to need him again. I put him up on a pedestal, denied my own needs and wants. Not good.
This has been said all over the board: "be the person he/she would be a fool to leave."
Me:57 H:52 M:28 Got another lawyer last year and filed. D35,S/D twins28,D22 EA4/04 End? Who knows? "Life is like a mirror. Smile at it and it smiles back at you." — Peace Pilgrim