What a sad situation for you. I suppose you’ve got two choices, he could get support from a local service and attend meetings etc.. with your support or you could leave and live a happy life for yourself without a selfish addiction dragging you down and making you unhappy.
I live with my partner who has a methadone script and it’s hard (even though he hasn’t relapsed) it’s taken a while and lots of ups and downs to get to this point. we have children and that is what stops me leaving. I do love him and want him to get better but it’s made me mentally and physically ill living with an addict so I’ve had to distance myself.
Could you consider either option?