Get your partner to be a SAHD, but only if you can trust him. That doesn't mean he has to do everything the way you want but a basic level of confidence in him is needed to do that.
My DP has complex CPTSD and quite bad social anxiety. He is so lovely though and being a SAHD suits us best. He wouldn't be a high earner or happy so it saves me the issue.
Sometimes I really miss working part time (there was a time in our life when he was at home and I was PT in the early years of our DCs lives and it was so lovely).
I remember to be grateful for what I have though, I've had 3 long mat leaves and many part time working patterns that have only relatively recently ended, and my PT working pattern only ended when I was working fully remotely so really I swapped one benefit for another.
You really shouldn't just be subsisting like this. Life is really hard at the moment, but your DH is making it harder.
As everybody has already said, he has 2 options to make your family life easier. He can give up on the SE venture and become a SAHP to your young DC, or he can give up the SE venture and get a job with an income which would allow you to go PT.
While the DC are young, I think you will regret not making the most of this pre school time. And once they are at school, things will be easier for both of you.
Is there any scope in your role for a flexible working pattern so you can take say, an afternoon a week off without dropping hours, or is there a possibility of doing some work at home?