How do you respond to him when he says he just wants to get it over with?
I've had to work through this over the past two years, and be open to anything that works. It can be a bit all over the place, depending on your relationship dynamic, is my guess.
There are some things you may, for your own mental health, decide to let go. And some things, you may not be ready for (letting go takes a lot of emotional strength!). It's good to have that stuff worked out firmly in your mind. If it's something you can let go, you have to figure out if you can go through the anguish of sticking to your boundary.
For example, if you feel sidelined over the custody stuff, and SO is not taking your input into consideration, then you may need to (for your own sake) explain that you can not participate in these discussions anymore because they make you feel xyz (sad, frustrated, angry, etc.) and that you need to take care of yourself so your cup stays full. You'll be a better partner to him, for example.
And then you have to be consistent -- if he brings up custody conversations, you may have to listen and nod your head, and validate how hard it is, and provide no input. Or tell him you need to hit pause, and while you wish you could help, it's too hard to witness and not have a voice.
I had to set a really hard boundary with my SO last summer that created conflict between us, and it took everything I had to follow through. And as unpleasant as it was, SO finally got it, after 4 years of negotiating over this particular boundary.
I told him my boundary ahead of time, when we were both calm and connected. I gave him a reminder when I saw the boundary infraction coming our way. I even encouraged him proactively to do something that would prevent the boundary from even being needed. Then, the boundary was breached and I stuck to my guns, without anger or pleading or negotiation. And because this was new behavior on my part, SO reacted strongly. I had to let him go through that without comforting him, and experience the unpleasantness of the boundary. Then magically, after a day or so, he began to proactively honor that boundary (he's a quick learner ).
If there is a better way to do this, I haven't found it yet.
Someone has to take care of you, may as well be you
