Oonana, I'm glad you and ex are managing to be civil to each other. I don't get the need to meet up for lunch, but if it suits you and you're both comfortable with it, then fine. Please just be careful it doesn't lead you back into an unhappy situation.
Bmthbelle, how gauche of DH's ex. Maybe it's to try to lord it over you or perhaps it's some crude attempt to make her present DH jealous. Whatever... The next time she tells such a story, I'd be tempted to, smilingly, of course, make some comment like, "Well, I guess none of that was good enough to make him stay," or "I'm glad you didn't go on making happy memories because now he and I are making outs." She may answer with a snappy comeback, but it it happens every time, she's likely to drop the habit. But I know that's not the usual advice, and maybe it's better to keep "quietly seething."