(1) You have no idea why XW is acting as she is. It is probably a good idea not to personalize it or take it as an attack on you. My own *guess* would be that she is upset thinking of her children having a stepmother and she feels scared and insecure. In reaction, she's choosing a fight rather than flight response. We don't seem to think that LBS's who freak out about an ex-spouses impending marriage and new step-parents entering the mix are out to hurt the ex-spouse and wanting the ex-spouse to stay lonely and miserable. Why put that stuff on XW?
(2) The lack of reasonable boundaries between you and XW is very inappropriate. You can't control XW, but you can choose how you interact with her. You can insist on texting and emails except for emergencies. And, texting 911 for emergencies is often more effective than a phone call. So, there is little, if any, reason for you to take XW's calls. There was zero reason for you to engage with XW and participate in the fight. "This conversation is inappropriate, bye."
(3) If I were your fiancee, I'd put things on hold until you are no longer enmeshed with W and you are able to set and enforce healthy boundaries in all your relationships and get to a healthy place of how to handle custody.
(4) If your XW made those statements about fiancee when your kids could hear, write it down. That is damaging to the children.
(5) Why are you unwilling to go through a psych evaluation?
You seem to be kind of all over the place on the custody stuff and in a pretty reactive mode in general. Focus on yourself.
