Hi OP, what's stopping you leaving is that you are thinking 'but it's only cannabis'.
Probably 9 times out of 10 I'd agree with that. But 9 out of 10 smokers are NOT like your DP. I've been around smokers for over 40 years and there have been stages in my life when I've been a regular smoker myself. Most people who smoke do so in the same way that most of us have the odd glass of wine or a couple of pints of beer. It doesn't have a negative impact on our lives. Even those I would say are heavy smokers (smoking most days, part of routine) live normal lives, do things, go out, go on holidays, go to work every day (I bet he doesn't) and have careers, raise happy healthy children, aren't miserable fuckers.
What you have there is the 1 out of 10 smokers, who is the smoker equivalent of an alcoholic. No control, no desire to stop, no ability to stop, a true addiction, and one that destroys their life. He literally cannot even go on a day out because of his habit? The thought of a week's holiday with his family without smoking is impossible to him? He is a loser. Men like this (and for some reason I've only seen men like this, and yes, I have seen them and their poor wives/families) do not ever change. One woman I know put up with this for over 20 years. She finally cracked and left him a couple of years ago, and she is free of being the only responsible one, the one who worked and supported them all, the one who bought their house, the one who lived essentially as a single parent with a loser in the house, the one who made all the effort, the one who had a career, while he sat indoors every day smoking his life away. She's so much happier now. In fact she's just become engaged and bought a nice little house with a nice man who adores her (not cannabis) and they have a great social life. Her kids have all done well, but it's thanks to her not her dad. She still smokes cannabis herself on occasion because she's one of the 9 out of 10 who isn't a jerk about it. She wishes she'd left her useless pothead ex years ago.
You can have a good normal life as a smoker. You can't as a pothead. Potheads never change. Never. This will be your life and your daughters life forever until you do something about it.