nlt, When a person feels insecure or threatened, they will do anything to keep their environment stable and yes, keep the spouse that they assisted in walking out the door. People who live lives of deceit, etc., are always looking over their shoulder and wondering when the spouse that left their home will walk again. After all, they both played in the adultery pool, so what makes either one of them think that it couldn't happen to them as well. Turn around is fair play.
The HO in your xh's life will screw up that little fantasy world in short order. She's already showing her hand and you know what? I would keep the emails, but I would try not to allow them to bother me because she's a "small" person in the scheme of things. She's nothing and it's evident that there is no class instilled in her upbringing.
N, you are a lady, a class act, and one that has been very hard for her to follow. Do not allow her to destroy your well being, for that's what she wants to do. Hug your pup this morning and know that you are loved by a lot of people. Her? She has nothing but fantasy, lies and deceit.