Don’t know if this will help or not…
Look for evidence. Huffing stuff will leave empty cans and towels it has been sucked through, which you can smell it on. Some of them you can use without the towel, but the empty can will still be there.
Be careful though with accusations. Yes, he might be hiding something, but accusing him of one thing might lead him to another thing.
I wish you nothing but the best.