Thanks everyone for the cont'd insight, offers of encouragement and for sharing your life stories.
Update:
After an additional text message sent reading "I told you to try to use my kids against me, I will go after you," I finally responded 3+ hours later with "Kids don't know anywhere near the extent of this," she called me. I asked if I could call her back so that I could start the VAR. Of course, a few minutes into the conversation, the VAR started giving a very loud and obnoxious echo like feedback. So, I turned it off.
The initial part of the conversation of course centered around the fact that the OM's wife now knows about the A and she told me that she was surprised that I'd do such a thing and that she wasn't expecting that from someone like me (still not sure what that means, but you may guess in a few). I told her that the OM's wife had every right to know. I told her that she'd want to know if she was being cheated on, right? No answer. She asked why I didn't call the OM directly. I said, why, so I can ask him how he enjoys fuc*ing my wife - hell no. Not much of a response to that. She then referred to what I did as a "bitch move." Okay, moving on as we are going nowhere with that.
A few seconds later we transition again back into all of my transgressions, how what she did was expected b/c she told me she needed someone who was going to love her and take care of her and that we really weren't "married" as she reminded me again about the times where she's asked for a separation. This went on for awhile as she basically threw everything against the wall to justify her actions while diminishing the severity of said actions, likening cheating to again, hiding alcohol, lying - you name it. She even mentioned drugs (pain killers), which is complete BS b/c she knows 100% that I don't mess w/prescrip pills, even after I had my knee surgery. It's almost like she had told this story so many times that it has snowballed into a bunch of lies and/or exaggerated facts, just to divert the responsibility back to me and to eliminate any accountability for her.
She then started w/the name calling and I disconnected the phone. I texted her that if she wants to act civil, we can talk at another time. Otherwise, I'd see her on Wednesday. She then called each of my oldest kids, separately, and had brief conversations. Nothing about her and I, just about them. She sounded sad - certainly not how she just sounded w/me (mad) or how she likely sounded w/the OM last night (ecstatic).
Fast forward 30 minutes, texts me and says that she's staying in tonight and not going out to dinner with the group as she's tired. Next text, "I'm sorry this all happened the way it did." At first, I was thinking (and was about to respond in kind), was this meant for me, or the OM, b/c that's who I believe she is feeling sorry for. Instead, I simply replied, "me too."
In full transparency, I don't even know who this person (my WW) is at this point. After 16 years, you would think that you'd know someone in their entirety, but it's almost like she's a completely different person. The lies, the cheating, the inability to take accountability, verbal cruelty, blaming etc. She couldn't give me a minute of her time yesterday to talk, now she spends almost the entire day trying to talk, change the narrative and make this my fault.
Anyway, that's a wrap for today. I don't have any regrets in reaching out to the OM's sister-in-law as that was my only way, and chance, of getting this news to OM's wife. I don't care that he's down in the dumps or that his marriage may be in trouble or if his wife just doesn't care. I just feel good that my WW is finally getting what they both deserve, even if just a little bit.