Trusting - some great comments here. I hope this makes you smile - my xh told me that what helped 'destroy' his r with OW [who he still sees btw] was that he kept coming back to me, and couldn't commit to her. Even that was somehow my fault. Strangely enough I couldn't feel apologetic about this.
Like AJ said, the r started on a poor foundation. She is needy and insecure, and it is all 'wrong'. But please detach, Your XH is still working through his stuff, and we none of us need more collateral damage.