The biggest thing you need to figure out is trust with your DH tank. Trust that he wouldn't talk to her behind your back, and that you're going to be informed. If you haven't already, talk with your DH and let him know your expectations on being informed when it comes to BM and Skids.

I used to be beyond paranoid too. I knew I couldn't tell him not to talk to the psycho, BUT, I also knew that I wasn't comfortable with it all. I had a talk with him, let him know that I expected communication to be solely about the skids, and only when necessary, anything else I saw an innapropriate. At first this was met with the "but it affects the kids!" But I was firm, and he did realize what I was saying, also around the time he realized she was trying to flirt with him and making gestures that were inappropriate, particualrly from a HCBM. I also made sure he knew I expected to be informed, because the most frustrating thing at the beginning was when it was days later and all the sudden I would get the "Oh! The ex messaged and she said such and such." And I was just sitting there going "When the f***ing he!! did this happen DH?" It was frustrating as heck.

For a while I still was a bit paranoid, and now honestly I'm terrified of her messaging some days (Always high conflict, always hurts the skids, it's a terrible cycle that makes me want to scream) BUT, I know I can trust DH to keep me informed, and that his loyalty is the one thing I don't need to worry about in this messed up step-situation.

... old song in my head (80's or 90's?). I say trust your gut, but also yes, PTSD. I suffered PTSD after a specific bizarre encounter years ago, and researched it a lot & also did counseling & EMDR therapy, which really helped me get past that specific anxiety. For me, the change was that instead of re-experiencing all the feelings, emotions, fears & anxieties when reminded of that event, I now remember it more like remembering a movie: recalling mentally instead of literally re-experiencing everything I felt (especially the paranoia & anxiety). 

Being a SM has brought a lot of the same ongoing, destructive anxiety & emotion. That's why I'm here on ST, learning from my PEEPS who totally get it!

Yes i used to have this all the time when BM was more active in SS's life. I still get it occasionally now even though theres not much she can do. It still creeps in. I also think its a ptsd thing. Mine was started from having a narc mother and the abuse from that then dealing with a narc BM is a trigger every time. 

Yes.

For me, I’d say it’s... triggering. It puts you on edge and makes you hyper aware of these feelings you’re having in your gut. Trust those instincts. You’ve been “here” before, so you know something is up or at least brewing on a very low setting. 

Things always seem off just before visitation and during, for me. I try my best to go radio silent during these times with my in-laws (the aggravators in my case) and DH (the enabler of the In-laws behavior). I write A LOT more, and keep detailed notes of certain unfavorable events around these times, in a protected online journal. It helps keep things in perspective. 

Your DH has a lot going on right now.  He is out of work.  His kids are in for a long visit.  His EX is HC and his current wife is highly sensitive to any situation involving his kids or his EX.  So, it would be natural for him to keep things to himself if he thinks you might react badly... but it could be anything.. job, kids, ex.. I would try to open the lines of communication and you will need to try to moderate your response.  You have conditioned him to not open up to you because you blow up over things.. even relatively minor things in his eyes...so he is now more guarded.

I always go with my gut, but my DH and I are working on trust issues. There are no longer any BM issues, but there are AA interloper biatches we deal with.

4 years ago, when SO and I had first started our relationship, after being friends for 1 1/2 years, things were pretty bad with a very Toxic BM She was always causing some kind of drama, about me, or how bad a father he is. So when she would text, I call it exactly PTSD. It got bad a year into our relationship, because she would drink and text him what he calls "zingers", and I caught one of them. And he deleted previous ones, so that eroded my trust. After I caught her inappropriate texts, he told her "stop doing that", she responded with "lucky for me my boyfriend isnt jealous", and he told her she needs to be respectful of me and our relationship. So supposedly she stopped. She still likes to tell him about her dating life (ewe) and she still likes to text him as if they are still friends (they were together 20 years).

Yes, when there is smoke, there is usually fire, too.