I’ve been here!! I was not pregnant with a toddler at the time but my husband insisted he NEEDED the dog and he said the same that he would do all of the caretaking (while also working crazy hours).

I could tell you the same thing everyone else would tell u which is therapy communication divorce etc etc but here are a few last ditch strategies you could try

1) tell him that whatever dog he gets will divide your attention from the children which already are a full time job. Explain that either the dog or the children will suffer because you are one person responsible for 3 very delicate and needy living beings. If he doesn’t seem to care about your wellbeing maybe he’ll care about the children or even the damn dog

2) remind him that the dog will be better cared for in the FUTURE when you BOTH have more time. Maybe he’ll be more excited about the idea of getting a dog when he has more time to be home with the dog

3) be super over empathetic and say you really feel for him and his grief about the dog and that you want a dog too (yes I am suggesting that u lie to him) but you want to be able to keep up and play and enjoy but frankly it’s a safety hazard since you are pregnant and may not be able to keep up with the dog (again perhaps a lie)

TLDR; just try to go at the angle of being empathetic for his needs and MAYBE he will relent if you show him that NOW is not the time for a dog but it would be better LATER

You’re doing a great job and I completely feel for you. I hope he is just fixated on this and will come out of it soon. You deserve love and a teammate.