I've caught up more on your thread and there were a couple things that stood out to me. Most of our situations here seem to at least contain similar elements, some even saying the same things verbatim. That said, reading your posts reminded me a lot of xw before bd. I had no idea about anything transpiring, MLC, nothing. During this time xw told me "I don't know what's wrong. Am I going crazy?" I reassured her no, I was clueless at the time. In hindsight I think this about when she decided to wade into the affair pool w/om. Also in hindsight, I started doing the wrong things shortly later as her crisis progressed. You got some really good advice about taking care of yourself right now, I don't think there is anything I could've done or said that would've helped. The only thing that did was taking care of myself and kids.
In regard to custody, I'm in a state that won't assign shared custody unless agreed upon by both parties and had to get a guardian attorney for custody recommendation. If there is no reason for you not to have your s don't roll over (trust me, being nice won't win her over, not saying not to be nice or civil but like so many say, treat it like business). Especially if you question your w's stability. I know my xw would never intentionally hurt the kids but she has. Her insanity was off the charts for awhile. I literally couldn't trust her to go to the grocery store. Do you think your w could get worse? I wouldn't agree to anything. Also, if you were to get custody you can always make it right. I did 50/50 after the recommendation was in my favor. I'm not saying that's right for everyone, but give yourself and your s what you deserve.