I'm in agreement with what others have said; this is a problem between the two of them. You getting involved is triangulating; not a healthy thing for any of you. That relationship is your STBX's to work on with her D.
As a mom with older, adult "kids", I will toss something else out there. They watch and learn from us and often use us as models for what to look for in a mate and how to behave in a relationship. Models for what is desirable and also for what is not desired. If your D has always learned that a woman should be faithful to one man and that is the view that STBX supported in view and/or behavior, your D is going to now view her as a liar. If a daughter suddenly realizes that she has been lied to by her own mother (or insert appropriate parent/child relationship here), the person who stayed home with her to instill so many of her values and beliefs; your D's entire worldview is now called into question. What else has mom said should be a certain way, but not followed herself? What is right?
Then she looks to you, as you are the other being that instills values. Are you still holding steady? If so, then mom is (again) behaving not in accordance with what the parental unit has said was right. This makes mom very, very wrong as she is not following her own teaching, has lied, and has hurt you (she is now going to be somewhat protective of the parent that hasn't disappointed her). Of course your D is angry with your STBX; she has betrayed her as a mother and betrayed her family by blowing it up. Your involvement in this relational problem on your STBX's behalf most likely will not help and may cause issues between you and your D. I've been there.
Your best bet is to give your D time to process her own feelings about things. As hard as it is, continue to only speak respectfully about STBX to kids (concentrate on the good, don't bring up the bad) and when they bring up bad behavior, phrase your views in regards to you and your behavior; try not to use STBX as an example of bad behavior. You can even opt out by saying, "I'm not responsible for what mom does." If pressed for your views, give them your beliefs, but again, not mentioning your STBX.
Yep. Your D will form her own thoughts and you don't need to intervene. If your STBX doesn't like the consequences of her actions, that is no longer your responsibility. Your responsibility is to have a good relationship with your kids and work on it yourself. She is responsible for hers.
Sorry so wordy. You'll get through this, Gordy. It does get better.
M-51 H-54 2D-27 and 25 M-26 yrs Bombshell and IHS 7-29-15 He moved out 10-3-15 D filed 1-27-16 D final 10-27-16
