I would suggest that you look at all the ways he's able to use.........and still keep his life together............then figure out just how much of it is because You or someone else is helping him/enabling him................then stop if you can so he can begin to feel and see for himself the effects of his drug use...............maybe then he can seek help
a starting place would be the .........come home and snorting part..........maybe set a limit right there and tell him no drugs in the house.......
Plus, theres a good change he does get it........but if he admits it he'd need to make changes and it doesnt sound like he's ready or willing so a good place for you to start is by making changes in the area you can control YOU!
..just my opinion.
good luck to you!!