It totally makes sense and I don't necessarily see anything wrong with the single exchange either. Just wanted to give him a word of caution to continue to think about the larger goal (detaching).
Agree.
I wouldn't give her nugglets of "feel good" or support while she is still carrying on with the OM(s). It does you no good.
If you pull away truly, she will feel the truth of their interaction and if they argue or she is disrespected she won't have you to wipe her feet on to feel better. She will feel the blows of that relationship.