"I am only rarely a fault finder/blamer, finding attributing fault and blame vindictive and unconstructive."
That's why NOTHING in your situation has changed. You don't do anything constructive about it. Instead, just let things lie where they are.
"Yes, I'd leave the hypothetical lousy M if d15 were not hurt by doing so. I stayed in the M out of fear, out of wanting to avoid conflict, out of loving the house and the situation here, out of a sense of duty (I promised, after all, for better or worse)."
BS. You stayed because you loved your W. Period. Stop blameshifting your reason for staying in the M all on her.
"I think my d15 finds me weird and not easy to be with sometimes. I imagine w has influenced d15's opinion of me, what with all she says"
Again that's BS. YOU are the one who influenced her decision of you. You said yourself that you don't know how to interact with her and your son. AND you've opted to live downstairs like a hermit for years. That's all YOUR choice. Not your W's.
"(I got mad at W this morning, btw, after she put down my college "
And so what did you TELL her? "Hence my feeling that it is not necessary or good to tell d15 anything just now."
And does your W know about this?
"Re mad, no, when W said "your thesis doesn't interest anyone", I said thanks, sarcastically, immediately after her POV."
Sarcasm isn't standing up for yourself. It's passive aggressive behavior.
"Hard to be with? D said a year or two ago "you have to ask me questions, Dad", so I do that now."
But the issue is that your D had to tell you that. It wasn't something that you just knew how to do.
You know you may find what I say to be "insulting" but have you ever considered EVEN ONCE, just trying what I suggest? Have you ever thought that the reason you've been on the track for divorce is because you HAVEN'T done what people have suggested to you? You do the same thing for years and what you want to do and nothing changes. And now you're blaming your W without looking inward.
M-43 W-40 2D - 9 and 5
Emotion, yet peace. Ignorance, yet knowledge. Passion, yet serenity. Chaos, yet harmony. Death, yet a new life.