You are who you associate with as much as you are what you eat.
Man, I wish I had a time machine.

But, you never know. Your friend's actions may be demonstrating to you very clearly what not to do, and although you seem already to have decided, his actions are only re-enforcing your wise decisions. Perhaps if he wasn't around you'd slip back into bad habits? Just trying to look at it positively, somehow.
I'm actually missing a small piece of my tongue (no, you'd never notice ...unless you're a lady and...) from a "dispute" I had with a friend, not that close though. Now he was
pissed and driving a few of us home. I said "WTF?". Argument ensued complete with fisty-cuffs. I lost slightly more.
After he dropped everyone off (luckily) he woke up in a ditch with a blanket on the passenger seat on fire from his ciggy. What an idiot.
I'm gonna guess you are in your 20's? It's pretty common to have a completely different set of friends at 30, if not standard practice.