Tim, that's a lot more involved than I ever imagined. I have no idea what I would do in a similar situation. You did your best. You're only human.
Unfortunately, your W has a lot of things to work through - there's an awful lot in her past and her behavior that sounds like recurring patterns. Unfortunately your MIL sounds like an enabler.
BTW, I wouldn't worry about S16 being poisoned - he'll resent you no matter what. He's just at that perfect age as was I. He's angry too, and has a lot to be angry about.
Well, everything you've been posting makes a lot more sense now. Unfortunately, you've got to put that oxygen mask on yourself first. Then you've got to decide who's next. I wouldn't want to be making that decision, but I know you'll make the right choice.
Go push yourself, exercise and detach - it's all you've got right now. And see if you can get some sleep - sometimes the subconscious can find solutions you never could.
Me: 58 Her: 59 Kids: 0 Dog: 1 ILYBINILWY: 9/15 D Bomb: 1/11/16 (found out filed) Verified OM: 1/11/16 Moved out: 1/11/16 (thought it was temporary)