Have you considered he may have never stopped with the pills and he's has been playing you along, the past 5 months? He's snorting. Next comes injecting. Often leads to heroin- better bang for the buck and all that.
There is nothing you can say or do that is going to get or keep him sober. You are not this powerful. None of us are. Recovery is 100% an inside job.
AA, NA, Salvation Army and assorted non- 12 step programs are readily available to him at any time.
Have you considered a firm boundary for yourself, " I don't do relationships with drug addicts or those who profess to be in early recovery". There is no pot of gold at the end of the rainbow for those who " stand bye their man/the chaos of addiction.