Need some advice

My husband loves to smoke pot. He's cut back a lot - probably because we fight a lot when he does smoke. I've asked him several times to stop. I've told him that I don't like the person he is, it doesn't taste good kissing him, and most importantly it affects our relationship every time he smokes. I've explained that every time he chooses pot over out relationship, he's actively damaging our relationship. It's been raining quite a bit here, and he's developed the habit of smoking before driving. Of course, it freaks me out because California drivers aren't the best in the rain and he's high so anything can happen. I've explained that to him, explained that we have a baby coming in 15 weeks, and asked him why he would jeapordize his life like that. He still doesn't seem to understand. He keeps saying that I'm trying to take away something he enjoys doing and he can't get past that. It's come to the point where I've told him that if he doesn't stop, I will limit his time with our son because I won't trust him. I do not want him to be high around our baby. I just don't know what to do anymore. I told him before we were married that I do not want pot or any drug in my life, and he continually disrespects me and our marriage. It's so strange because he such a good man in every other regard. It's this vice that is causing a major roadblock, and I'm starting to resent him for it.