Hi super girl. I'm not in same boat now but i have experience.
Myself and partner were heavy drugs user's, cannabis was my thing and narcotics were his. He'd been taking drugs from 12 years old.
I was in care and chose cannabis and alcohol as a way to cope with what happened to me. Before I was with my partner I smoked and drank everyday at 15 years old, I felt I couldn't get through the day without it. My mother begged me to stop social workers and friends and relatives pleaded with me to wise up before I ruined my life but I never payed any attention. When you have N addiction whether it be a physical addiction or psychological addiction to something it becomes your priority and it's what you will put first.
Fast forward a while I met dp through taking drugs. He was 21 very heavy drinker and drug taker he took Meth and coke everyday while holding down full time job.
We got on great both loved drink and drugs (should add dp stopped smoking cAnnabis a long time before he met me due to paranoia) but eventually the realisation hit home when my bipolar became very unstAble as I was paranoid, deluded ND depressed, my fAmily stopped speaking to me because I was always high. I attempted to take my own life because I couldn't deal with everything going on in my head especially when not high. This made me realise it was time to stop. I stopped drinking and smoking but it was so hard especially when it's the one thing you look forward too everyday and if he has friends who smoke it will make it a hell of alot harder for him.
In the end my dp decided it was time for us both to change he stopped drink and drugs and so did I but we HD to holster ourselves from everyone we knew who took drugs to stop temptations ago h was hard as it meant cutting off people we cared about.
Fast forward 3 years I'm now 19 and 23 weeks pregnant and he's 24 and we are both completely off drugs and drink and I don't drink at all now. We're completely stable but we needed each others support to get through it.
If he's no motivation or will power to stop it you a fighting a losing battle as he has to choose and if you force him he will take it out on you.
I just wanted to tell you my story so u know it is possible for him to change but he has to want it and be willing to on his own.
I hope you can get him help but from him smoking it ten years he will be best to cut down gradually instead of straight away as if they just stop it normally doesn't last.
Try sitting down without and discussing phasing out the cannabis, so if he's having one a day now set timeline for him to stop completely if he's willing to,
So say one a day now for next week and then one every other day and so on it may help to show u support him but make it clear that u will not tolerate the constant use of it any more.
Good luck x