It was not, and often still isn't, easy. I had to bite my tongue a lot. And it's very hard to walk that line between being a doormat and giving them some room to maneuver around the debris they've created in their own minds and in our lives, while preserving our self-respect.
Your response about D was good. The hardest thing for me was accepting the paperwork from the process server without saying anything. I tended to give one-word responses - it was much easier via text, though. I really thing that it was important that I didn't "create any drama" as she likes to say. Like so many on here, and like MWD has mentioned, the very act of her going through with starting that process, and my reaction to it, seems to have caused her to stop and think about what she was doing, and the permanence of it. It was right then that she started being more friendly in our interactions.
Hope I didn't blather on too much. The real key, I think is to remember to be validating, stay off the subject yourself as much as possible, and keep it brief.
