And, oh my God, your mother is going through cancer treatment and has two schoolage children at home?
OP, you CANNOT sleep on a sofa with a newborn. I'm serious, that's incredibly dangerous. And you CANNOT go to your mother's, generally, that's totally out of line. You will need help and support, you will need understanding, you will need to be able to stay awake in the middle of the night and sleep during the day, you will be tender and probably bleeding and leaking and hormonal. It's a time when you want to have your walls around you, your own cosy nest, your things and your space.
He is being totally fucking selfish. I don't care if you love him, a man who is spending half his wage (HALF?) on weed, smoking in the flat with you, his pregnant partner, in the same space, hasn't bought anything or shared incomes with you, and now wants you to fuck off while he makes merry on his own. So he can sleep.
Oh, OP. This needs sorting. This is so far out of line I don't even have the words.