I think exposure is the right thing to do for my own self-respect. In addition, it's important to me that certain people understand what is happening.
So, his parents; her aunt; and their place of work get exposure from me. i.e. You should know that your son (and other S and DIL) will be responsible for blowing up my marriage and the effects on our D; work gets -prepare for potential moral and/or harassment issues. They are blowing up my marriage and when (not if) the A implodes, you need to C your A; her aunt- an explanation that though I'm 50% responsible for the deterioration, the reason it died is the A. She has lied for months to me so I want you to know the truth cause she'll lie to you, too. If she doesn't bring D around enough, let me know and I will.
One exposure. And I'm done trying to save anything. The Great Race is over. She lost.