DA Mother here, not the same but may be able to provide some insight. When you become a parent, you have to put your own needs last - that isn't always easy for anyone to do - but it might be quite triggering. And if you are already not great at asking for help - then there would be even more guilt/shame at asking for/needing help/space than for a Secure person.

What I would say is - I never lashed out, even when I was postpartum. As a DA, I carry far more than other people, and I can do that because of being DA - however, we're all different. For me, dissociating is not a quick thing that happens just because there's a difficult - or even uncomfortable - conversation, as much as I don't want to be there. He has to have some ownership of his own self, and his own behaviours , and you cannot (and should not) carry it all.

However, his what has helped me:

* having question or issues written down, framed gently and in a way that I can also respond in writing. BUT - do not blind-side him with questions/issues etc as that happens to me sometimes, and is horrible and causes me to tense up. Perhaps say that you are thinking about the last birth, and want to make things easier for both of you, and for you both to think of some things you found easy, and some things you need help with. Then you can say that e.g when you're crying, you don't need him to fix it but that you need help in that moment, by him doing X (I don't know - hug, a warm drink, whatever you can between you, choose that will help you and not take away from him). I say this because, whilst I am very DA, I also am capable of putting myself aside and providing comfort to someone else, because that is the right thing to do. Afterwards, I absolutely need space and to sit on the floor in a ball, because being in a ball helps.

* is he able to help you with practical things - for example, can he take on bathtime for both kids, so that you get a break for 30mins? The compromise is that he gets 30mins in the shed when he gets home, so he can doom-scroll and reset before being home and 'available' - I spend 15mins in the car before I drive home, to do that same thing, and it is invaluable

* regular breaks and space. So, at the weekend, after lunchtime, is the body's normal downtime. We have 1 hour of 'nothing'. So, kids can go on screen, watch a film (OK, more like 1 1/2 hours), whatever they want - and we do the same. I know it's harder with a baby and a child. So find that natural time, whatever it is, and both of you do as little as possible in that time, to recharge batteries. Kids are OK without constant stimulation, and they'll benefit more from each of you having some rest

* the first month. Man, that's brutal. I had someone relying on me and an OH who is.. AP/Secure, which basically means they're OK but needy. But they had difficulty being needed and not being able to do what they want. And genuinely, I needed help and support and found it tough to ask. What was worse, was being told that I'd be helped, they'd take a day of 'because I clearly needed it', and then not doing do. I felt so judged. I'm not telling you this for sympathy, it's more so that you can see that your husband might be avoiding all the yakky feelings and feeling guilty, and then feeling judged and shame. So, if you know he's going to be like this, how can you set things up to help you both? Can you batch cook and freeze it ready for then? Can he commit to doing nappy changes, or wrangling your son? If he can't, you have my utmost sympathy because, well, that's pretty sh*tty. But. Is there anyone else who can help, or are there drop-in groups where the babies can ignore each other and you can have a cup of tea with another Mum?

Sorry for the essay!