You said in your opening post he has been smoking weed consistently since he was 18 & he is now 32. Im guessing he also smoked weed before the age of 18 but not consistently. He has been consistently smoking weed for all of his adult life. He also moderately drinks alcohol & has admitted to trying cocaine a few times, but very occasionally.
I read what you wrote how you feel about him. I understand that part.
Something however obviously has gone very wrong here. You ended up moving out & living with your parents. You posted your story on SR F & F Substance Abuse Forum. You didnt post your story on some type of unconditional love or romance forum.
Do you believe he is an addict?
If the answer to that question is yes - then you need to think through what if you go back to him & find weed. Chances are you will find weed. The only reason he says he stopped is because of you. He didnt stop for his own good. He stopped because you left & forced him into it (at least so he says) His brother also now has stopped. What about all those friends have they stopped? Can he be around those friends while they get high and not do it himself?
Addiction is no small stumbling block to a relationship. Its a major ugly in your face type problem. Oh its only weed. Yeah thats today. What happens tomorrow more coke maybe hit of crystal meth? The train often goes totally off the tracks dramatically & suddenly.
This is your life, its not mine. I can only hope you will think this through. I went back numerous times. Each time when the bad happened again, I lost more of myself. Each & every time I went back it got worse way worse. Hoping you wont make the same mistakes as I did.