DH refused to talk to BM about anything except SD. If she started talking about her own life, he would tell her he was going to hang up on her. She was very manipulating and always had an ulterior motive. She eventually got the hint.

He has not talked to BM since SD got married at 18 and CS ended.

I can see being civil in front of the kids for the kids, but that's different than being friends. Sadly, BM was not interested in that, she was always a total bitch in front of SD.

My h's boundaries with BM are non-existent.
I'm always having to tell him what to say when she calls and he over-shares and gives her too much info. They still text and talk about SD's who are 18 and 23, which I find absurd. When my boys are 18 my exh's phone number will be lost forever.
Ex's need to communicate about the minor kids and the kids only, those are my suggestions. That is what I communicate with my ExH, and that's all the communication we have.
BM used to feel free to come in my house and I had to put a stop to that as well. It's MY house and she is not welcome.

DH had to actually tell BM "we are NOT friends, we will never be friends, we were not friends when we were together which is a HUGE reason we didn't work out I am SS's DAD, and you are his MOM and that is ALL. Don't call me for advice about your jobs, or relationships, or your family. WE ARE NOT FRIENDS". It got better after that, but.... it still took her a while to understand that just because she is SS's mom doesn't mean she has any kind of say in our house. That one had to be spelled out for her too.

Our relationship boundary:
SO is not allowed to have any private relationships with any other women, and I am not allowed to have private relationships with men. I tell him about every text, email or conversation with my ex, and he tells me about the ones with his.

Rules for BM:

1. She cannot have his cell phone number. WE got his number changed two years ago after too many texts and a fake emergency in which she interrupted our date to say that she was taking the skid to the hospital, and then refused to answer her phone all night. The kid didn't even go to the hospital.

2. She cannot call him at work. This took A LOT longer for me to get him to do, but it was worth it in the end and he agrees. It took at least 5 arguments over two years, and then I had to kick his ass out and write an email explaining my stance to him, cc'ing his mother, before he understood I was not playing. YOU DON'T TAKE PHONE CALLS FROM CRAZY PEOPLE EVER. He needs a paper trail! Plus, she cannot think that she has a private relationship (connection) with him because it gives her validity. She needs to know how little she means! She would call out of the blue and ask for "BM favors" rather than "skid favors", then shame/slander him when he didn't comply. That's crap and she doesn't deserve access simply for shitting out a kid.

3. Email ONLY communication about the kids. This was recently put into a temporary court order and I couldn't be more pleased! Hard won, let me tell ya. He already told her a few months ago that this is what he wanted. He now forwards EVERY email from her to me, we talk about it, think about it, and come up with a proper response - if at all!

4. I have no communication with her. After her stalking and harassment and three trips to the police station, I think she finally realizes that she shouldn't eff with me anymore.

All in all, BM cannot talk to SO at all unless it is in writing. I read everything. And her communication that was ever-so-important before, has tapered off to a once a month email that may or may not get responded to. Put the attention whore right back in her cage where she belongs.