Thanks for your feedback, guys.
When I came home last night, John told me he thought about it and agreed that a break should happen, but he didn't know when. I said - how about November 4th. But this can't just be a break from sexting and alone time, it needs to be a break from all communication so they can both develop coping skills and not be so dependent on each other for support.
Then I asked him to tell me exactly what his needs are, which he had never really done. He started by saying he needed his texts with Sarah to be completely un-limited (in frequency and type of content), and a couple of other things. And I stopped him and said - do you absolutely need to have a romantic relationship with Sarah - meaning that without that need being met, he and I would get a divorce.
He said he thought his answer was yes, but he's not completely sure.
So I clairified - so you mean that even if it we determine that a continued relationship with Sarah would destroy us, you'd choose Sarah over us?
He said he'd have to think about it.
I absolutely need our relationship to be our first priority - for no other relationship to come before ours. So right now we are on the edge of a knife for ending our marriage.
I was so upset and crying so hard that I couldn't breathe, and my limbs started to get pins and needles. John got me a bag to breathe in and helped me to the couch. Today we have plans with friends (including Sarah) so I'm just trying to hold it all together the best I can. I gave Sarah the short short version of what's happened, but with everybody around that's all I had time for.