Like everyone touched by infidelity, your sister has put you in a terrible position. She has put EVERYONE in a terrible position without One. Single. Thought. About how she was endangering the family livelihood and reputation, about how she was hurting her BS and her child, about how she was destroying another family too. Does this sound like a person who’s going to magically come around when confronted with an ultimatum?
You are absolutely doing the right thing in exposing them, BUT. . .the other posters are right. Cheaters lie. It is the single most consistent thing about them. They ALL lie. It is a pre-condition of cheating. Whatever she says to you in that phone call, it’s very unlikely it will be true.
If you’ve had the misfortune of needing this amazing site full of people who know much more about this than they ever wanted to, you realize very quickly how repetitive certain themes and actions on the part of the WS are. One is that you NEVER get the full story up front. Another is that, once discovered, WSs move immediately and seamlessly into CYA mode. This includes a VAST amount of minimizing and denying. That is where your sis will be tomorrow. Where she will NOT be is accepting that she has to just come clean with everyone and start trying to figure out her shit. She has been willing to harm her own child and other children to do this. She won’t just immediately see that it has to be over and that she never should have let herself get attached to him and that she’s put everyone in harm’s way.
She will not reach immediate remorse and acceptance. She WILL absolutely contact the OM to try to get stories straight, minimize damage, and try to figure out the minimum she can say. She WILL absolutely try to make it sound like you are WAY overdramatizing what is going on. She will not tell her BS everything, and she will absolutely deny anything that can’t be directly proven (and may even try to deny that until completely backed against the wall).
She may one day begin to understand how wrong she is here and how much damage she has done, but please understand that time won’t be tomorrow. Tomorrow she will be absolutely panicked with fear and anger. She will be in absolute defense mode. It’s just how it goes—how it ALWAYS goes.
You already know that she thinks she can control you into saying nothing, and you already know that she doesn’t want to stop the A. She doesn’t want it exposed. Be prepared for hostility and viciousness. You will not recognize her, as you’ve said. You may not for a long time. I never saw the person who even a little reminded me of my former H once his A was revealed. He was a stranger who remained exactly that. He lied to himself about what he was doing and the damage he might be causing. He couldn’t face any of it, and he fought back hard and dirty against anyone who tried to make him face it or reminded him of what a shit he’d been.
The people who should be told before her are your dad and her BS and the other man’s BS. They are the victims whose lives have been forever altered by this horribly selfish course. She is not someone who can be counted on to care about them right now. She won’t care about anyone but herself.
There is a long road ahead for her to figure her shit out. It’s generous of you to offer PT and a chance to do the right thing, but she just won’t be ready for any of that this quickly. Maybe keep those things at the ready for a little more down the road.
Either way, you’ve made such a caring and honest decision here. That is huge. I wish you peace and a clear head tomorrow to figure out what you should do and keep your wits and resolve about you.
Sending you a huge hug of support and strength. We’ll be here however it turns out.