The wrong people as in the people that enabled his habit, rather than helping him to break it.
I'd say being around guys like Mainwaring was habit forming. The proof, unfortunately for chris, was in the pudding.
It's Ben's fault, but the culture around him exacerbated his problem more than it helped.
The fact CM may have been a "great bloke" aside.
(and if you want to get technical, drug possession is actually a crime, so he was...)