This is not your fault Sleepy. When me and DH had a harsh talk about issues with his ex I told him I don't care what games he and his ex want to play. If he wants to stand by and allow her to manipulate and weaponize their son then he is no better but I am not letting our daughter get dragged in. I don't care about winning I want me and DD out of it and happy.
Had no issues with his ex recently. Not sure if he gets a hard time. I don't want him unhappy but at some point I just had to let it go. I can't fight his battles for him if he isn't going to do something.
Forget your DH and step child for a moment and think what is best for you and your own baby and go with that, whatever that decision is. Is it better for you and your baby to talk to DH and give him time to improve (say a month)? Is it better to walk away? Is it better to deal with changes in plans and carry on as you are?
That's what I do now. I think "is this the best for me and DD?". Things are getting better. I feel so sorry for my SS and many SCs as they are completely innocent and the step mums and dads are doing their best but because the actual parents can't sort things out.
I'm always telling my DH he needs to learn to talk to his ex. She does shitty things like passing off her own husband as dad, changing times pick ups and he just lets her because he is afraid of losing access. Obviously SS needs to see his dad but I've told DH if she tries to stop get your bloody court order and take to police or judge because his son needs healthy relationship with both parents not seeing this mess. Better for SS in long term to have DH be firm and miss out for a couple of weeks than years of this rubbish (I know not good for SS to miss out and if his mother twists then she is a cow but saying sorting it out once and for all is the lesser evil than phases of banned access).
The only nag I am okay with is DH does all the pick ups and drop offs because I don't want her around me and DD or our home so it works for me and DD.
I don't want my DH or DSS to suffer just to suffer but as selfish as it is I always ring fence me and DD first and then worry about them now. An example is I'm on maternity. I could have DSS over to spend more time with his sister but because ExW sends abusive texts in the past I won't give her my number. No number means I can't arrange having DSS over extra times. DSS wants my number and I had to say no (I did not say why).
I told DH let ExW we can control our own home. DSS knows me and his step dad are equal, that daddy and mummy are equal. We say good things about his mum and step dad. It's a shame because before DH met me (Ex had been with her DH for 3 years?) DH, his ex, her DH and DSS never did anything together. I would facilitate the five of us having food together, meeting up with ExW and DSS to make friends and she completely ruined that. DH has been bad at times too. Becuase DH and his ExW won't try and work together me and DSS step dad have ended up arguing and I told DH it's mad.
But now DH knows me and DD are on one side, his ex and her DH is on the other and there is no crossover. As long as e and DD are ok then that is all I can do.