C.S.
I am actually a step-mom...my husband and I have been together for 8 years and I am 6 years younger than he is. My husband had it stated in their divorce decree that no one else would be called mom or dad - this is an important issue to all of us. We have all (including the step-dad) made sure this is how it is.
Ironically, I do most of the communicating with my huband's ex. Not due to a controlling issue (which she might think it is sometimes), but because it's just easier for us now. I stay at home, my husband is a busy business man who travels quite a bit, who doesn't like to deal with details. So, if we need to switch time or whatever, I e-mail her or call her. We do have an unusual relationship. (When my step-son doesn't have school or during the summers, she brings him over here on her 2 weeks to stay for the day while she is at work.) We've had to build this; this definitely didn't happen over night. I comletely agree that this isn't right for her to be doing. She is obviously not mature enough to handle this situation and realize that her selfish needs for control shouldn't come first.
The biggest thing that my husband taught me (from day one!) was that my step-son was always first...just as our 2 daughters now are as well. You obviously believe this as well. This isn't because he loved my step-son more or because he was lingering in his past relationship, but because he was a child and he needed his parents - both parents. I am so sorry to hear what you are going through and I truly hope that your ex gets his act together to realize what is going on and that they both realize who is most important.
Unfortunatley, I don't have much advice to offer, but it sounds like your ex has changed and I can't imagine what you are going through, but I wish you the best!