10 yrs of hell

My Stepson has been using Cocaine for 10 yrs, he has lost 10 yrs of his life & has the mindset of a 17 yr old. In 11 yrs he has been sacked from 12 jobs for not turning up, due to drug benders. We have tried the hard, soft, understanding, supportive approaches but seem to get nowhere. We have now discovered that he doesn’t actually want to stop doing drugs and have decided that he’s made his choice in life but it’s hard to turn your back on someone who’s “hungry” and begging for food even though you know, deep down, that any money they have is going on drugs not food. Feeling very guilty and blaming ourselves!