Sorry you are going through this stress, it does sound like your partner doesnt know or understand how to have a civilised discussion about things and takes everything the wrong way, if this has been going on for a long time to varying extents then it sounds like hes not just going to suddenly change on his own, he may not even agree that hes actually doing it and thats the hardest thing to try and work with as it is very unlikely to ever change
One thing I will say aswell and I hope it doesnt offend anyone is that I have never seen anything good become of anyone who smokes weed, in fact Ive seen people heading towards depression, anxiety, anger issues and even psychotic breakdowns from it, the best case scenario Ive seen is people becoming unmotivated losers, it also will not set a good example for your child to be around that, it does not sound like you are on that wavelength of recreationally smoking weed whereas he is
I know youve said you want a loving stable family and Im guessing you would prefer a two parent family, can totally understand that as thats what I would prefer to but what you might need to think about is which environment will be better for the child, sometimes single parent is a hell of a lot better then two parents fighting like cat and dog, children pick up on these tensions very acutely and it becomes a huge source of anxiety for them
I think youve got to weight it all up really, but do not be afraid to leave if your heart tells you thats the right thing to do, it will be different difficult at first but you will get through it and come out on the other side xx