I guess the different directions, WhyUs, are part of recognising that it isn't a simple thing in either cause or effect. Even if there seem to be some common patterns in what we see and share.
My take on the 'illness' issue fwiw. I think most of us initially see them as 'mentally ill' bc their behaviour is so extreme or unfamiliar and want to 'help' them. Hence the debates here about accountability and forgiveness etc. Imho these folks do experience a kind of breakdown and do behave in many ways that have roots in depression, anxiety or mania. However, what helped me was when a friend of mine whose husband was a recovered alcoholic said to me that I should treat him like an addict who was not ready to deal with his addiction. That it did not make the behaviour any more acceptable to live with, that he was responsible for his addiction or recovery, but it might help me to be able to think of him in a way that separated the person I loved from the addict he was now. And that if he ever stopped behaving like an addict and showed up in recovery, I could decide how I felt about the recovered addict then. I found that quite helpful in both plotting my course and in deciding how I felt about the person he was compared to who he is. And of course the common ground in both situations is that I cannot help an addict who does not want to stop being an addict.....and true too that a recovered addict is not the same person exactly as they were before addiction ran the show.
So, I guess, with my long-gone h, it doesn't feel much different from if he were lost in an alcohol fuelled dump or slumped somewhere with a needle in his arm. I am very sad about it and i have no idea if he will ever get well. Or if he will show up in my life again in some form if he does. I can pray for him and I suppose I can decide if I will open my door and listen if he recovers or not. That's about it. It got to a point when it was too painful to watch so it is easier that he has gone.
I am also aware that framing it that way may be quite inaccurate or a bit of denial lol but it is the only way I can keep my own memory of who he was which matters to me, so hey ho. The universe may give me new information sometime that challenges that picture and if so, I'll adapt to that then.
I don't think every spouse here has had this kind of great unravelling breakdown.
But, on balance, i suspect my h probably did and if he wants to recover, I guess the complexity of why and how is more his business than mine.
But I recognise most of the ingredients you listed as part of your xw's MLC dish, the oppositeness that is so strange to witness. Conway I think was about right....job, body, spouse and God are the four basic pillars that they play with in trying out a new self in this process....some more than others...but it comes out in some very strange ways as you say. Respected Catholic nurse and mother to Devil-guided Vampire Teenage Princess as you say, there does seem to be a teenager flavour to most.....
From the little I can see, my xh went from Small Village Aspiring Vicar And Community Good Guy with Cats to Athiest Wannabe Big Swinging City Cool d!ck with a Crazy Drama Blonde
T: 18 M: 12 (at BD) No kids.
H diagnosed with severe depression Oct 15. BD May 16. OW since April 16, maybe earlier. Silent vanisher mostly.
Divorced April 18. XH married ow 6 weeks later.
"Option A is not available so I need to kick the s**t out of Option B" Sheryl Sandberg