Welcome to SR from a fellow Tennessean!! (Did I spell that right??) I just got my final divorce decree from a man who used to smoke pot just the way you are describing (and possibly worse....). He used to smoke from the time he got up to the time he went to bed and I mean all day long. He did finally give up the pot, but he never gave up the drugs; I have found pills in various places for the last 15 years. He, too, always promised to change, but never did. He might stay clean for a few months, but before long he would be using again. What jerked me into reality was realizing in January of 2006 that my 53-year-old husband was crushing up pills and snorting them. Ugh.
We were together for 29 years, married for 26 (almost) and have three sons together. One of them has already graduated from college, is married and has one daughter and another baby on the way. One of them is a college sophomore. And one of them is in the fifth grade.
I say all that to say this-it's just not worth it to live with someone in active addiction. Don't think for one minute that your child won't be affected because he will. I would bet my life that, even at 8, he already knows way more than you think he does. I speak from sad experience.
You do not have the power to make this man do or not do anything. You are young and your child needs you. It won't be easy because you are so enmeshed with this guy and I will promise you that he will pull out all kinds of tricks to get you to stay. You will be blamed for every bad thing that he does and for every bad thing that happens to him. It is awful to listen to someone you care about beg you not to leave them and tell you how much they hurt and cry that you can save them. You can't. You just can't.
Keep reading and posting and know that you are among people who understand.
(((HUGS)))